Water / wastewat. (conveyance) / Vodov. i kanal.

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Water and Wastewater Conveyance

The design considerations for the piping system are the function of the specifics of the system. However, all piping systems have a few common issues: the pipe strength must be able to resist internal pressure, handling, and earth and traffic loads; the pipe characteristics must enable the pipe to withstand corrosion and abrasion and expansion and contraction of the pipeline (if the line is exposed to atmospheric conditions); engineers must select the appropriate pipe support, bedding, and backfill conditions; the design must account for the potential for pipe failure at the connection point to the basins due to subsidence of a massive structure; and the composition of the pipe must not give rise to any adverse effects on the health of consumers.1

8.1 DELIVERING THE LIFEBLOOD OF CIVILIZATION Conveyance or piping systems resemble veins, arteries and capillaries. According to Nayyar, “they carry the lifeblood of modern civilization. In a modern city they transport water from the sources of water supply to the points of distribution; convey waste from residential and commercial buildings and other civic facilities to the treatment facility or the point of discharge.”2 Water and wastewater operators must be familiar with piping, piping systems, and the many components that make piping systems function. Operators are directly concerned with various forms of piping, tubing, hose, and the fittings that connect these components to create workable systems.

This chapter covers important, practical information about the piping systems that are a vital part of plant operation, essential to the success of the total activity. To prevent major system trouble, skilled operators are called upon to perform the important function of preventive maintenance to avoid major breakdowns, and must be able to make needed repairs when breakdowns do occur. A comprehensive knowledge of piping systems and accoutrements is essential to maintaining plant operations.

8.2 CONVEYANCE SYSTEMS In regard to early conveyance systems, the prevailing practice in medieval England was the use of closed pipes. This practice was contrary to the Romans who generally employed open channels in their long-distance aqueducts

and used pipes mainly to distribute water within cities.

The English preferred to lay long runs of pipes from the water source to the final destination. The Italians, on the other hand, where antique aqueduct arches were still visible, seem to have had more of a tendency to follow the Roman tradition of long-distance channel conduits. At least some of the channel aqueducts seem to have fed local distribution systems of lead or earthenware pipes.3 With today’s water and wastewater conveyance, not much has changed from the past. Our goal today remains the same: (1) convey water from source to treatment facility to user, and (2) convey wastewater from user to treatment to the environment.

In water and wastewater operations, the term conveyance or piping system refers to a complete network of pipes, valves, and other components. For water and wastewater operations in particular, the piping system is all-inclusive; it includes both the network of pipes, valves, and other components that bring the flow (water or wastewater) to the treatment facility, as well as piping, valves and other components that distribute treated water to the end user and treated wastewater to outfall. In short, all piping systems are designed to perform a specific function.

Probably the best way to illustrate the importance of a piping system is to describe many of its applications used in water and wastewater operations. In the modern water and wastewater treatment plant piping systems are critical to successful operation. In water/wastewater operations, fluids and gases are used extensively in processing operations; they usually are conveyed through pipes. Piping carries water and wastewater into the plant for treatment, fuel oil to heating units, steam to steam services, lubricants to machinery, compressed air to pneumatic service outlets for air-powered tools, etc., and chemicals to unit processes.

In water treatment alone, Kawamura points out that there are “six basic piping systems: (1) raw water and finished waste distribution mains; (2) plant yard piping that connects the unit processes; (3) plant utility, including the fire hydrant lines; (4) chemical lines; (5) sewer lines; and (6) miscellaneous piping, such as drainage and irrigation lines.”4 Besides raw water, treated water, wastewater influent, and treated wastewater effluent, the materials conveyed through piping systems include oils, chemicals, liquefied gases, acids, paints, sludge, and many others.

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Important Point: Because of the wide variety of materials that piping systems can convey, the components of piping systems are made of different materials and are furnished in many sizes to accommodate the requirements of numerous applications. For example, pipes and fittings can be made of stainless steel, many different types of plastic, brass, lead, glass, steel, and cast iron.

Any waterworks or wastewater treatment plant has many piping systems, not just the systems that convey water and wastewater. Along with those mentioned earlier, keep in mind that plant-piping systems also include those that provide hot and cold water for plant personnel use.

Another system heats the plant, while another may be used for air conditioning.

Water and wastewater operators have many responsibilities and basic skills. The typical plant operator is skilled in heating, ventilation, and air conditioning systems; chemical feed systems, and mechanical equipment operation and repair in piping system maintenance activities.

However, only the fluid transfer systems are important to us in this text. The units that the piping system serves or supplies (such as pumping, unit processes, and machines) are discussed in other chapters of the text.

For water and wastewater operators, a familiar example of a piping system is the network of sodium hypochlorite pipes in treatment plants that use this chemical for disinfection and other purposes. The whole group of components — pipes, fittings, and valves — working together for one purpose makes up a system. This particular system

Elbow

Check valve

Tee fitting Coupling

Union

Check valve

has a definite purpose — to carry sodium hypochlorite and distribute it, conveying it to point of application.

Note: This chapter is concerned only with the piping system used to circulate the chemical, not with the hypochlorination equipment itself. Our concern begins where the chemical outlet is connected to the storage tank and continues to the point where the pipe is connected to the point of application. The piping, fittings, and valves of the hypochlorination pipeline (and others) are important to us. Gate, needle, pressure-relief, air-and-vacuum relief, diaphragm, pinch butterfly, check, rotary and globe valves, traps, expansion joints, plugs, elbows, tee fittings, couplings, reducers, laterals, caps, and other fittings help ensure the effective flow of fluids through the lines. As you trace a piping system through your plant site, you will find many of them (see Figure 8.1). They are important because they are directly related to the operation of the system.

Piping system maintenance is concerned with keeping the system functioning properly, and to function properly, piping systems must be kept closed and leak proof.

Important Point: Figure 8.1 shows a single-line diagram that is similar to an electrical schematic. It uses symbols for all the diagram components. A double-line diagram (not shown here) is a pictorial view of the pipe, joints, valves and other major components similar to an electrical wiring diagram, instead of an electrical schematic.

Gate valve

Reduced

Lateral

Cap

45° Elbow

90° Elbow (turned down)

FIGURE 8.1 Shows various components in a single-line piping diagram. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

© 2003 by CRC Press LLC

Water and Wastewater Conveyance

8.2.1 DEFINITIONS Key terms related to water and wastewater conveyance are listed and defined in this section.

Absolute pressure gauge pressure plus atmospheric pressure.

Alloy a substance composed of two or more metals.

Anneal to heat and then cool a metal in order to make it softer and less brittle.

Annealing process of heating and then cooling a metal, usually to make it softer and less brittle.

Asbestos fibrous mineral form of magnesium silicate.

Backsiphonage a condition in which the pressure in the distribution system is less than atmospheric pressure, which allows contamination to enter a water system through a cross-connection.

Bellows a device that uses a bellows for measuring pressure.

Bimetallic made of two different types of metal.

Bourbon tube a semicircular tube of elliptical cross section, used to sense pressure changes.

Brazing soldering with a nonferrous alloy that melts at a lower temperature than that of the metals being joined; also known as hard soldering.

Butterfly valve a valve in which a disk rotates on a shaft as the valve opens and closes. In the full open position, the disk is parallel to the axis of the pipe.

Carcass the reinforcement layers of a hose, between the inner tube and the outer cover.

Cast iron a generic term for the family of high carbonsilicon-iron casting alloys including gray, white, malleable, and ductile iron.

Check valve a valve designed to open in the direction of normal flow and close with reversal of flow.

An approved check valve has substantial construction and suitable materials, is positive in closing, and permits no leakage in a direction opposite to normal flow.

Condensate steam that condenses into water in a piping system.

Diaphragm valve a valve in which the closing element is a thin, flexible disk often used in low-pressure systems.

Differential pressure the difference between the inlet and outlet pressures in a piping system.

Double-line diagram pictorial view of the pipes, joints, valves, and other major components similar to an electrical wiring diagram.

Ductile a term applied to a metal that can be fashioned into a new form without breaking.

Expansion joint absorbs thermal expansion or contraction in piping systems. Š 2003 by CRC Press LLC

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Extruding process of shaping a metal or plastic by forcing it through a die.

Ferrous a term applied to a metal that contains iron.

Ferrule a short bushing used for making a tight connection.

Filter an accessory fitting used to remove solids from a fluid stream.

Fluids any substance that flows.

Flux used in soldering to prevent the formation of oxides during the soldering operation and to increase the wetting action so solder can flow more freely.

Friable readily crumbled by hand.

Gate valve a valve in which the closing element consists of a disk that slides across an opening to stop the flow of water.

Gauge pressure the amount by which the total absolute pressure exceeds the ambient atmospheric pressure.

Globe valve a valve having a round, ball-like shell and horizontal disk.

Joint a connection between two lengths of pipe or between a length of pipe and a fitting.

Laminar flow arranged in or consisting of thin layers.

Mandrel a central core or spindle around which material may be shaped.

Neoprene a synthetic material that is highly resistant to oil, flame, various chemicals, and weathering.

Metallurgy the science and study of metals.

Nominal pipe size the thickness given in the product material specifications or standard to which manufacturing tolerances are applied.

Nonferrous a term applied to a material that does not contain iron.

Piping systems a complete network of pipes, valves, and other components.

Ply one of several thin sheets or layers of material.

Prestressed concrete concrete that has been compressed with wires or rods in order to reduce or eliminate cracking and tensile forces.

Pressure-regulating valve a valve with a horizontal disk for automatically reducing water pressures in a main to a preset value.

PVC polyvinyl chloride plastic pipe.

Schedule approximate value of the expression 1000 P/S, where P is the service pressure and S is the allowable stress, both expressed in pounds per square inch.

Single-line diagram uses symbols for all the diagram components.

Soldering a form of brazing in which nonferrous filler metals having melting temperatures below 800ÂşF (427ÂşC) are used. The filler material is called solder and is distributed between surfaces by capillary action.

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Solenoid an electrically energized coil of wire surrounding a movable iron case.

Stainless steel an alloy steel having unusual corrosion-resisting properties, usually imparted by nickel and chromium.

Strainer an accessory fitting used to remove large particles of foreign matter from a fluid.

Throttle controlling flow through a valve by means of intermediate steps between fully open and fully closed.

Tinning covering metal to be soldered with a thin coat of solder to work properly. Overheating or failure to keep the metal clean causes the point to become covered with oxide. The process of replacing this coat of oxide is called tinning.

Trap an accessory fitting used to remove condensate from steam lines.

Vacuum breaker a mechanical device that allows air into the piping system thereby preventing backflow that could otherwise be caused by the siphoning action created by a partial vacuum.

Viscosity the thickness or resistance to flow of a liquid.

Vitrified clay clay that has been treated in a kiln to produce a glazed, watertight surface.

Water hammer the concussion of moving water against the sides of pipe, caused by a sudden change in the rate of flow or stoppage of flow in the line.

8.2.2 FLUIDS

VS.

LIQUIDS

We use the term fluids throughout this text to describe substances being conveyed through various piping systems from one part of the plant to another. We normally think of pipes conveying some type of liquid substance, which most of us take to have the same meaning as fluid, but there is a subtle difference between the two terms. The dictionary’s definition of fluid is any substance that flows — which can mean a liquid or gas (air, oxygen, nitrogen, etc.). Some fluids carried by piping systems include thick viscous mixtures, such as sludge, in a semifluid state. Although sludge and other such materials might seem more solid (at times) than liquid, they do flow, and are considered fluids.

In addition to carrying liquids such as oil, hydraulic fluids, and chemicals, piping systems carry compressed air and steam, which also are considered fluids because they flow.

Important Point: Fluids travel through a piping system at various pressures, temperature, and speeds. © 2003 by CRC Press LLC

8.2.3 MAINTAINING FLUID FLOW IN PIPING SYSTEMS The primary purpose of any piping system is to maintain free and smooth flow of fluids through the system. Another purpose is to ensure that the fluids being conveyed are kept in good condition (i.e., free of contamination).

Piping systems are purposely designed to ensure free and smooth flow of fluids throughout the system, but additional system components are often included to ensure that fluid quality is maintained. Piping system filters are one example, and strainers and traps are two others.

It is extremely important to maintain free and smooth flow and fluid quality in piping systems, especially those that feed vital pieces of equipment and machinery. Consider the internal combustion engine, for example. Impurities such as dirt and metal particles can damage internal components and cause excessive wear and eventual breakdown.

To help prevent such wear, the oil is run continuously through a filter designed to trap and filter out the impurities.

Other piping systems need the same type of protection that the internal combustion engine does, which is why most piping systems include filters, strainers, and traps.

These filtering components may prevent damage to valves, fittings, the pipe, and to downstream equipment/machinery. Chemicals, various types of waste products, paint, and pressurized steam are good examples of potentially damaging fluids. Filters and strainers play an important role in piping systems, protecting both the piping system and the equipment that the piping system serves.

8.2.3.1 Scaling Because sodium and calcium hypochlorite are widely used in water and wastewater treatment operations, problems common in piping systems feeding this chemical are of special concern. In this section, we discuss scaling problems that can occur in piping systems that convey hypochlorite solution.

To maintain the chlorine in solution (used primarily as a disinfectant), sodium hydroxide (caustic) is used to raise the pH of the hypochlorite; the excess caustic raises the shelf life. A high pH caustic solution raises the pH of the dilution water to over pH 9.0 after it is diluted. The calcium in the dilution water reacts with dissolved CO2 and forms calcium carbonate. Experience has shown that 2-in. pipes have turned into 3/4-in. pipes due to scale buildup. The scale deposition is greatest in areas of turbulence such as pumps, valves, rotameters, backpressure devices, etc.

If lime (calcium oxide) is added (for alkalinity), plant water used as dilution water will have higher calcium levels and generates more scale. While it is true that softened water will not generate scale, it is also true that it is expensive in large quantities. Many facilities use softened water on hypochlorite mist odor scrubbers only.

Water and Wastewater Conveyance

Scaling also often occurs in solution rotameters, making flow readings impossible and freezing the flow indicator in place. Various valves can freeze up and pressuresustaining valves freeze and become plugged. Various small diffuser holes fill with scale. To slow the rate of scaling, many facilities purchase water from local suppliers to dilute hypochlorite for the return activated sludge (RAS) and miscellaneous uses.

Some facilities have experimented with the system by not adding lime to it. When they did this, manganese dioxide (black deposits) developed on the rotameter’s glass, making viewing the float impossible. In many instances, moving the point of hypochlorite addition to downstream of the rotameter seemed to solve the problem.

If remedial steps are not taken, scaling from hypochlorite solutions can cause problems. For example, scale buildup can reduce the inside diameter of pipe so much that the actual supply of hypochlorite solution required to properly disinfect water or wastewater was reduced. As a result, the water sent to the customer or outfalled to the receiving body may not be properly disinfected. Because of the scale buildup, the treatment system itself will not function as designed and could result in a hazardous situation in which the reduced pipe size increases the pressure level to the point of catastrophic failure. Scaling, corrosion, or other clogging problems in certain piping systems, are far from an ideal situation.

EXAMPLE 8.1 For explanation purposes, the scale problem is taken a step further by use of example. Assume that we have a piping system designed to provide chemical feed to a critical plant unit process. If the motive force for the chemical being conveyed is provided by a positive-displacement pump at a given volume of solution at 70 psi through clean pipe. After clogging takes place, the pump continues trying to force the same volume of chemical through the system at 70 psi, but the pressure drops to 25 psi. Friction caused the pressure drop. The reduction of the inside diameter of the pipe increased the friction between the chemical solution and the inside wall of the pipe.

Important Point: A basic principle in fluid mechanics states that fluid flowing through a pipe is affected by friction — the greater the friction, the greater the loss of pressure.

Important Point: Another principle or rule states that the amount of friction increases as the square of the velocity. (Note: speed and velocity are not the same, but common practice refers to the velocity of a fluid.) In short, if the velocity of the fluid doubles, the friction is quadrupled compared to what it was before. If the velocity © 2003 by CRC Press LLC

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is multiplied by 5, the friction is multiplied by 25, and so on.

In Example 8.1, the pressure dropped from 70 to 25 psi because the solution had to run faster to move through the pipe. Because the velocity of the solution pushed by the pump had to increase to levels above what it was when the pipe was clean, the friction increased at a higher rate than before. The fiction loss was the reason that a pressure of 25 psi reached the far end of the piping system. The equipment designed to operate at a pressure of 70 psi could not work on the 25 psi of pressure being supplied.

Important Point: After reviewing the previous example, you might ask: Why couldn’t the pump be slowed down so that the chemical solution could pass more slowly through the system, thus avoiding the effect of increased friction?

Lower pressure results as pump speed is reduced. This causes other problems as well.

Pumps that run at a speed other than that for which they are designed do so with a reduction in efficiency.

What is the solution to our pressure loss problem in Example 8.1? Actually, we can solve this problem two possible ways: either replace the piping or clean it.

Replacing the piping or cleaning it sounds simple and straightforward, but it can be complicated. If referring to a pipe that is relatively short, no more than 20 to a few hundred feet in length, then we may decide to replace the pipe. What would we do if the pipe were 3 to 5 mi or more in length? Cleaning this length of pipe probably makes more sense than replacing its entire length. Each situation is different, requiring remedial choices based on practicality and expense.

8.2.4 PIPING SYSTEM MAINTENANCE Maintaining a piping system can be an involved process.

Good maintenance practices can extend the life of piping system components and rehabilitation can further prolong their life.

The performance of a piping system depends on the ability of the pipe to resist unfavorable conditions and to operate at or near the capacity and efficiency that it was designed for. This performance can be checked in several ways: flow measurement, fire flow tests, loss-of-head tests, pressure tests, simultaneous flow and pressure tests, tests for leakage, and chemical and bacteriological water tests.

These tests are an important part of system maintenance.

They should be scheduled as part of the regular operation of the system.5 Most piping systems are designed with various protective features, including minimizing wear and catastrophic failure, and therefore the amount of maintenance

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required. Such protective features include pressure relief valves, blow-off valves, and clean-out plugs.

1. Pressure relief valves — A valve that opens automatically when the fluid pressure reaches a preset limit to relieve the stress on a piping system.

2. Blow-off valve — A valve that can be opened to blow out any foreign material in a pipe.

3. Clean-out plug — A threaded plug that can be removed to allow access to the inside of the pipe for cleaning.

Valves also function as protective devices. For example, valves used to protect a piping system may be designed to open automatically to vent fluid out of the pipe when the pressure in the lines becomes too high. In lines that carry liquids, relief valves preset to open at a given pressure are commonly used.

Important Point: Not all valves function as safety valves. For example, hand-operated gate and globe valves function primarily as control valves.

The correct size and type of valve is selected for each use. Most valves require periodic inspection to ensure they are operating properly.

Important Point: Use caution when removing a clean-out plug from a piping system. Before removing the plug, pressure must be cut off and the system bled of residual pressure.

8.2.6 PIPING SYSTEM ACCESSORIES

Many piping systems (including water distribution networks and wastewater lines and interceptors) can be cleaned either by running chemical solvents through the lines or by using mechanical clean-out devices.

8.2.5 VALVES Depending on the complexity of the piping system, the number of valves included in a system can range from no more than one in a small, simple system to a large number in very complex systems such as water distributions systems. Valves are necessary for both the operation of a piping system and for control of the system and system components. In water and wastewater treatment, this control function is used to control various unit processes, pumps, and other equipment.

Along with valves, piping systems typically include accessories such as pressure and temperature gauges, filters, strainers, and pipe hangers and supports.

1. Pressure gauges — These gauges show what the pressure in the piping system is.

2. Temperature gauges — These gauges show what the temperature in the piping system is.

3. Filters and strainers — These accessories are installed in piping systems to help keep fluids clean and free from impurities.

4. Pipe hangers and supports — These accessories support piping to keep the lines straight and prevent sagging, especially in long runs. Various types of pipe hangers and supports are shown in Figure 8.2.

Adjustable pipe roll stand Anchor chair

Adjustable swivel pipe roll

Standard ring and bolt hanger

Adjustable clevis and band hanger

FIGURE 8.2 Pipe hangers and supports. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.) © 2003 by CRC Press LLC

Water and Wastewater Conveyance

8.2.7 PIPING SYSTEMS: TEMPERATURE EFFECTS Most materials, especially metals, expand as the temperature increases and contract as the temperature decreases.

This can be a significant problem in piping systems. To combat this problem, and to allow for expansion and contraction in piping systems, expansion joints must be installed in the line between sections of rigid pipe. An expansion joint absorbs thermal expansion and terminal movement; as the pipe sections expand or contract with the temperature, the expansion joint expands or compresses accordingly, eliminating stress on the pipes.

8.2.8 PIPING SYSTEMS: INSULATION You do not need to wander too far in most plant sites to find pipes covered with layers of piping insulation. Piping insulation amounts to wrapping the pipe in an envelopment of insulating material. The thickness of the insulation depends on the application. Under normal circumstances, heat passes from a hot or warm surface to a cold or cooler one. Insulation helps prevent hot fluid from cooling as it passes through the system. For systems conveying cold fluid, insulation helps keep the fluid cold.

Materials used for insulation vary, and they are selected according to the requirements of application. Various types of insulating materials are also used to protect underground piping against rusting and corrosion caused by exposure to water and chemicals in the soil.

8.3 METALLIC PIPING Pipe materials that are used to transport water may also be used to collect wastewater. It is more usual, however, to employ less expensive materials since wastewater lines rarely are required to withstand any internal pressure. Iron and steel pipe are used to convey wastewater only under unusual loading conditions or for force mains (interceptor lines) in which the wastewater flow is pressurized.6

8.3.1 PIPING MATERIALS Materials selected for piping applications must be chosen with the physical characteristics needed for the intended service in mind. For example, the piping material selected must be suitable for the flow medium and the given operating conditions of temperature and pressure during the intended design life of the product. For long-term service capability, the material’s mechanical strength must be appropriate; the piping material must be able to resist operational variables such as thermal or mechanical cycling. Extremes in application temperature must also be considered in respect to material capabilities.

Environmental factors must also be considered. The operating environment surrounding the pipe or piping components affects pipe durability and life span. Corrosion, © 2003 by CRC Press LLC

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erosion, or a combination of the two can result in degradation of material properties or loss of effective loadcarrying cross section. The nature of the substance contained by the piping is also an important factor.

Knowledge of the basic characteristics of the metals and nonmetals used for piping provides clues to the uses of the piping materials with which we work in water and wastewater treatment operations. Such knowledge is especially helpful to operators, making their job much easier and more interesting. In this section, metallic piping is discussed. Piping joints, how to join or connect sections of metallic piping, and how to maintain metallic pipe are also discussed.

8.3.2 PIPING: THE BASICS Earlier, we pointed out that piping includes pipes, flanges, fittings, bolting, gaskets, valves, and the pressure-containing portions of other piping components.

Important Point: According to Nayyar, “a pipe is a tube with round cross section conforming to the dimensional requirements of ASME B36.10M (Welded and Seamless Wrought Steel Pipe) and ASME B36.19M (Stainless Steel Pipe).”7 Piping also includes pipe hangers and supports and other accessories necessary to prevent overpressurization and overstressing of the pressure-containing components.

From a system viewpoint, a pipe is one element or a part of piping. Accordingly, when joined with fittings, valves, and other mechanical devices or equipment, pipe sections are called piping.

8.3.2.1 Pipe Sizes With time and technological advancements (development of stronger and corrosion-resistant piping materials), pipe sizes have become standardized and are usually expressed in inches or fractions of inches. As a rule, the size of a pipe is given in terms of its outside or inside diameter.

Figure 8.3 shows the terminology that applies to a section of pipe. Pipes are designated by diameter. The principal dimensions are: Wall thickness

O.D.

I.D.

Length FIGURE 8.3 Pipe terminology. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

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1. Wall thickness 2. Length 3. Outside diameter (O.D.) — used to designate pipe greater than 12 in. in diameter 4. Inside diameter (I.D.) — used to designate pipe less than 12 in. in diameter Important Point: Another important pipe consideration not listed above or shown in Figure 8.3 is weight per foot, which varies according to the pipe material and pipe’s wall thickness.

In the continuing effort to standardize pipe size and wall thickness of pipe, the designation nominal pipe size (NPS) replaced the iron pipe size designation; the term schedule (SCH) was developed to specify the nominal wall thickness of pipe.

The NPS diameter (approximate dimensionless designator of pipe size) is generally somewhat different from its actual diameter. For example, the pipe we refer to as a 3-in. diameter pipe has an actual O.D. of 3.5 in., while the actual O.D. of a 12-in. pipe may be .075 in. greater (i.e., 12.750 in.) than the nominal diameter. On the other hand, a pipe 14 in. or greater in diameter has an actual O.D. equal to the nominal size. The inside diameter will depend upon the pipe wall thickness specified by the schedule number.

Important Point: Keep in mind that whether the O.D. is small or large, the dimensions must be within certain tolerances in order to accommodate various fittings.

8.3.2.2 Pipe Wall Thickness Original pipe wall thickness designations of STD (standard), XS (extra-strong), and XXS (double extra-strong) are still in use today; however, because this system allowed no variation in wall thickness, and because pipe requirements became more numerous, greater variation was needed. As a result, pipe wall thickness, or schedule, today is expressed in numbers (5, 5S, 10, 10S, 20, 20S, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160). (Note: You will often hear piping referred to either in terms of its diameter or Schedule number.) The most common schedule numbers are 40, 80, 120, and 160. The outside diameter of each pipe size is standardized. Therefore, a particular nominal pipe size will have a different inside diameter depending upon the schedule number specified. For example, a Schedule 40 pipe with a 3-in. nominal diameter (actual O.D. of 3.500 in.) has a wall thickness of 0.216 in.

The same pipe in a Schedule 80 (XS) would have a wall thickness of 0.300 in.

Important Point: A schedule number indicates the approximate value of the expression 1000 P/S, © 2003 by CRC Press LLC

where P is the service pressure and S is the allowable stress, both expressed in pounds per square inch (psi). The higher the schedule number, the thicker the pipe is.

Important Point: The schedule numbers followed by the letter S are per ASME B36.19M, and they are primarily intended for use with stainless steel pipe.8 8.3.2.3 Piping Classification The usual practice is to classify pipe in accordance with the pressure-temperature rating system used for classifying flanges. However, because of the increasing variety and complexity of requirements for piping, a number of engineering societies and standards groups have devised codes, standards, and specifications that meet most applications. By consulting such codes, (e.g., American Society for Testing and Materials [ASTM], Manufacturer’s Specifications, National Fire Protection Association [NFPA], American Water Works Association [AWWA], and others), a designer can determine exactly what piping specification should be used for any application.

Important Point: Because pipelines often carry hazardous materials and fluids under high pressures, following a code helps ensure the safety of personnel, equipment, and the piping system.

8.3.2.3.1 ASTM Ratings ASTM publishes standards (codes) and specifications that are used to determine the minimum pipe size and wall thickness to use in given application.

8.3.2.3.2 Manufacturer’s Rating Pipe manufacturers, because of propriety design of pipe, fitting, or joint, often assign a pressure-temperature rating that may form the design basis or the piping system. (Note: In addition, the manufacturer may impose limitations that must be adhered.)

Important Point: Under no circumstances shall the manufacturer’s rating be exceeded.

8.3.2.3.3 NFPA Ratings Certain piping systems fall within the jurisdiction of NFPA. These pipes are required to be designed and tested to certain required pressures (usually rated for 175 psi, 200 psi, or as specified).

8.3.2.3.4 AWWA Ratings AWWA publishes standards and specifications that are used to design and install water pipelines and distribution system piping. The ratings used may be in accordance with the flange ratings of AWWA, or the rating could be based upon the rating of the joints used in the piping.

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8.3.2.3.5 Other Ratings Sometimes a piping system may not fall within the above related rating systems. In this case, the designer may assign a specific rating to the piping system. This is a common practice in classifying or rating piping for main steam or hot reheat piping of power plants, whose design pressure and design temperature may exceed the pressuretemperature rating of ASME B16.5. In assigning a specific rating to such piping, the rating must be equal to or higher than the design conditions.

Important Point: The rating of all pressure-containing components in the piping system must meet or exceed the specific rating assigned by the designer.9 When piping systems are subjected to full-vacuum conditions or submerged in water, they experience both the internal pressure of the flow medium and external pressure. In such instances, piping must be rated for both internal and external pressures at the given temperature.

Moreover, if a piping system is designed to handle more than one flow medium during its different modes of operation, it must be assigned a dual rating for two different flow media.

8.3.3 TYPES

OF

PIPING SYSTEMS

Piping systems consist of two main categories: process lines and service lines. Process lines convey the flow medium used in a manufacturing process or a treatment process (such as fluid flow in water and wastewater treatment). For example, one of the major unit process operations in wastewater treatment is the sludge digestion. The sludge is converted from bulky, odorous, raw sludge to a relatively inert material that can be rapidly dewatered with the absence of obnoxious odors. Because sludge digestion is a unit process operation, the pipes used in the system are called process lines.

Service lines (or utility lines) carry water, steam, compressed air, air conditioning fluids, and gas. Normally, all or part of the plant’s general service system is composed of service lines. Service lines cool and heat the plant, provide water where it is needed, and carry the air that drives air equipment and tools.

8.3.3.1 Code for Identification of Pipelines Under guidelines provided by the American National Standards Institute (ANSI-A 13.1 [current date]), a code has been established for the identification of pipelines.

This code involves the use of nameplates (tags), legends, and colors. The code states that the contents of a piping system shall be identified by lettered legend giving the name of the contents. In addition, the code requires that information relating to temperature and pressure should Š 2003 by CRC Press LLC

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be included. Stencils, tape, or markers can be used to accomplish the marking. To identify the characteristic hazards of the contents, color should be used, but its use must be in combination with legends.

Important Point: Not all plants follow the same code recommendations, which can be confusing if you are not familiar with the system used. Standard piping color codes are often used in water and wastewater treatment operations. Plant maintenance operators need to be familiar with the pipe codes used in their plants.

8.3.4 METALLIC PIPING MATERIALS In the not too distant past, it was not (relatively speaking) that difficult to design certain pipe delivery systems. For example, several hundred years ago (and even more recently in some cases) when it was desirable to convey water from a source to point of use, the designer was faced with only two issues. First, a source of fresh water had to be found. Next, if the source were found and determined suitable for whatever need required, a means of conveying the water to point of use was needed.

In designing an early water conveyance system, gravity was the key player. This point is clear when you consider that before the advent of the pump, a motive force to power the pump, and the energy required to provide power to the motive force were developed, gravity was the means by which water was conveyed (with the exception of burdened humans and animals that physically carried the water) from one location to another.

Early gravity conveyance systems employed the use of clay pipe, wood pipe, natural gullies or troughs, aqueducts fashioned from stone, and any other means that was suitable or available to convey the water. Some of these earlier pipe or conveyance materials are still in use today.

With the advent of modern technology (electricity, the electric motor, the pump and various machines and processes) and the need to convey fluids other than water, also came the need to develop piping materials that could carry a wide variety of fluids.

The modern waterworks has a number of piping systems made up of different materials. One of the principal materials used in piping systems is metal. Metal pipes may be made of cast iron, stainless steel, brass, copper, and various alloys. As a waterworks or wastewater maintenance operator who works with metal piping, you must be knowledgeable about the characteristics of individual metals as well as the kinds of considerations common to all piping systems. These considerations include the effect of temperature changes, impurities in the line, shifting of pipe supports, corrosion, and water hammer.

In this section, we present information about pipes made of cast iron, steel, copper, and other metals. We also

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discuss the behavior of fluids in a piping system, and the methods of connection sections of pipe.

8.3.4.1 Characteristics of Metallic Materials Different metals have different characteristics, making them usable in a wide variety of applications. Metals are divided into two types: ferrous, which includes iron and iron-base alloys (a metal made up of two or ore metals which dissolve into each other when melted together); and nonferrous, which covers other metals and alloys.

Important Point: Mixing a metal and a nonmetal (e.g., steel, which is a mixture of iron (a metal) and carbon (a non-metal) can also form an alloy.

Metallurgy (the science and study of metals) deals with the extraction of metals from ores and with the combining, treating, and processing of metals into useful materials.

A ferrous metal is one that contains iron (elemental symbol Fe). Iron is one of the most common of metals, but is rarely found in nature in its pure form. Comprising about 6% of the earth’s crust, iron ore is actually in the form of iron oxides (Fe2O3 or Fe3O4). Coke and limestone are used in reduction of iron ore in a blast furnace where oxygen is removed from the ore, leaving a mixture of iron and carbon and small amounts of other impurities. The end product removed from the furnace is called pig iron — an impure form of iron. Sometimes the liquid pig iron is cast from the blast furnace and used directly for metal castings. However, the iron is more often remelted in a furnace, to further refine it and adjust its composition.10 Important Note: Piping is commonly made of wrought iron, cast iron, or steel. The difference among them is largely the amount of carbon that each contains.

Remelted pig iron is known as cast iron (meaning the iron possesses carbon in excess of 2% weight). Cast iron is inferior to steel in malleability, strength, toughness, and ductility (i.e., it is hard and brittle). Cast iron has, however, better fluidity in the molten state and can be cast satisfactorily into complicated shapes.

Steel is an alloy of iron with no more than 2.0% by weight carbon. The most common method of producing steel is to refine pig iron by oxidation or impurities and excess carbon, both of which have a higher affinity for oxygen than iron. Stainless steel is an alloy of steel and chromium.

Important Note: When piping is made of stainless steel, an “S” identifies it after the schedule number.

Various heat treatments can be used to manipulate specific properties of steel, such as hardness and ductility (meaning it can be fashioned into a new form without © 2003 by CRC Press LLC

breaking). One of the most common heat treatments employed in steel processing is annealing. Annealing (sometimes referred to as stress-relieving) consists of heating the metal and permitting it to cool gradually to make it softer and less brittle.

Important Point: Steel is one of the most important basic production materials of modern industry.

Unlike ferrous metals, nonferrous metals do not contain iron. A common example of a nonferrous metal used in piping is brass. Other examples of nonferrous materials used in pipe include polyethylene, polybutylene, polyurethane, and PVC. Pipes11 of these materials are commonly used in low-pressure applications for transporting coarse solids.

In addition to the more commonly used ferrous and nonferrous metals, special pipe materials for special applications are also gaining wider use in industry, even though they are more expensive. Probably one of the most commonly used materials that falls into this category is aluminum pipe. Aluminum pipe has the advantage of being lightweight and corrosion-resistant with relatively good strength characteristics.

Important Note: Although aluminum is relatively strong, it is important to note that its strength decreases as temperature increases.

Lead is another special pipe material used for certain applications, especially where a high degree of resistance to corrosive materials is desired. Tantalum, titanium, and zirconium piping materials are also highly resistant to corrosives.

Piping systems convey many types of water, including service water, city water, treated or processed water, and distilled water. Service water, used for flushing and cooling purposes, is untreated water that is usually strained, but is otherwise raw water taken directly from a source (e.g., lake, river, or deep well). City water is treated potable water. Treated water has been processed to remove various minerals that could cause deterioration or sludge in piping. Distilled water is specially purified.

Important Point: Piping materials selection for use in water treatment and distribution operations should be based on commonly accepted piping standards such as those provided by ASTM, AWWA, ANSI, the American Society of Mechanical Engineers, and the American Petroleum Industry.

8.3.4.1.1 Cast-Iron Pipe According to AWWA, “there are more miles of [cast-iron pipe] in use today than of any other type. There are many water systems having cast-iron mains that are over 100 years old and still function well in daily use.”12 The advantages of cast-iron pipe are that it is strong, has a

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long service life, and is reasonably maintenance-free. The disadvantages include its being subject to electrolysis and attack from acid and alkali soils and its heaviness.13 8.3.4.1.2 Ductile-Iron Pipe Ductile-iron pipe resembles cast-iron pipe in appearance and has many of the same characteristics. It differs from cast-iron pipe in that the graphite in the metal is spheroidal or nodular form —in ball-shape form rather than in flake form. Ductile-iron pipe is strong, durable, has high flexural strength and good corrosion resistance, is lighter than cast iron, has greater carrying capacity for same external diameter, and is easily tapped. However, ductile-iron pipe is subject to general corrosion if installed unprotected in a corrosive environment.14 8.3.4.1.3 Steel Pipe Steel pipe is sometimes used as large feeder mains in water-distribution systems. It is frequently used where there is particularly high pressure or where very large diameter pipe is required. Steel pipe is relatively easy to install; has high tensile strength, lower cost, and is good hydraulically when lined; and is adaptable to locations where some movement may occur. However, it is subject to electrolysis external corrosion in acid or alkali soil, and has poor corrosion-resistance unless properly lined, coated, and wrapped.

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8.3.5.1 Expansion and Flexibility Because of thermal expansion, water and wastewater systems (which are rigid, and laid out in specified lengths) must have adequate flexibility. In water and wastewater systems without adequate flexibility, thermal expansion may lead to failure of piping or anchors. It may also lead to joint leakage and excessive loads on appurtences. The thermal expansion of piping can be controlled by use of proper locations of anchors, guides, and snubbers. Where expansion cannot be controlled, flexibility is provided by use of bends, loops, or expansion joints.15 Important Point: Metals expand or contract according to temperature variations. Over a long run (length of pipe), the effects can cause considerable strain on the lines — damage or failure may result.

8.3.5.2 Pipe Support Systems Pipe supports are normally used to carry dead weight and thermal expansion loads. These pipe supports may loosen in time, so they require periodic inspection. Along with normal expansion and contraction, vibration (water hammer and/or fluids traveling at high speeds and pressures) can cause the supports to loosen.

Note: The materials of which street wastewater (sewer) pipes are most commonly constructed are vitrified clay pipe, plastic, concrete, and ductile iron pipe. However, it is metallic ductile iron pipe that is most commonly used in wastewater collection, primarily for force mains (interceptor lines, etc) and for piping in and around buildings. Ductile iron pipe is generally not used for gravity sewer applications, however.

8.3.5.3 Valve Selection

8.3.5 MAINTENANCE CHARACTERISTICS OF METALLIC PIPING

8.3.5.4 Isolation

Maintenance of metallic piping is determined in part by characteristics of the metal (i.e., expansion, flexibility, and support), but also includes the kind of maintenance common to nonmetallic piping systems as well. The major considerations are: 1.

2.

3.

4.

5.

6.

7.

8.

Expansion and flexibility Pipe support systems Valve selection Isolation Backflow prevention Water hammer Air binding Corrosion effects

© 2003 by CRC Press LLC

Proper valve selection and routine preventive maintenance is critical in the proper operation and maintenance of any piping system. In water and wastewater-piping systems, valves are generally used for isolating a section of a water main or wastewater collection line, draining the water or wastewater line, throttling liquid flow, regulating water or wastewater storage levels, controlling water hammer, bleeing off of air, or preventing backflow.

Various valves are used in piping systems to provide for isolation. For instance, gate valves are used to isolate specific areas (valve closed) of the system during repair work or to reroute water/wastewater flow (valve open) throughout the distribution or collection system. Service stop valves are commonly used to shut off service lines to individual homes or industries. Butterfly valves are also used for isolation purposes.

8.3.5.5 Preventing Backflow Backflow, or reversed flow, could result in contaminated or polluted water entering the potable water system. There are numerous places in a water distribution system where unsafe water may be drawn into the potable water mains if a temporary vacuum should occur in the system. In

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Manufacturing Process Wastewater 60 PSIG

Reclaimed wastewater Wastewater Treatment Process

30 PSIG Public water supply FIGURE 8.4 Shows backflow from recirculated system. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

addition, contaminated water from a higher-pressure source can be forced through a water system connection that is not properly controlled. A typical backflow condition from recirculated system is illustrated in Figure 8.4.

Important Point: Valves, air gaps, reduced-pressurezone backflow preventers, vacuum breakers, and barometric loops are often used as backflowprevention devices, depending on the situation.

8.3.5.6 Water Hammer In water and wastewater operations specifically involving flow through piping, we often hear the term water hammer used. The term water hammer (often called surging) is actually a misnomer in that it implies only water and the connotation of a hammering noise. However, it has become a generic term for pressure wave effects in liquids.

By definition, water hammer is a pressure (acoustic) wave phenomenon created by relatively sudden changes in the liquid velocity. In pipelines, sudden changes in the flow (velocity) can occur as a result of (1) pump and valve operation in pipelines, (2) vapor pocket collapse, or (3) even the impact of water following the rapid expulsion of air out of a vent or a partially open valve.16 Water hammer can damage or destroy piping, valves, fittings, and equipment.

Important Point: When water hammer occurs, there is little the maintenance operator can do except to repair any damage that results.

8.3.5.7 Air Binding Air enters a piping system from several sources. These include air being released from the water, air being carried in through vortices into the pump suction, air leaking in through joints that may be under negative pressure, and air being present in the piping system before it is filled. © 2003 by CRC Press LLC

The problem with air entry or air binding, because of air accumulation in piping, is that the effective cross-sectional area for water/wastewater flow in piping is reduced. This flow reduction can, in turn, lead to an increase in pumping costs through the resulting extra head loss.

8.3.5.8 Corrosion Effects All metallic pipes are subject to corrosion. Many materials react chemically with metal piping to produce rust, scale, and other oxides. In regards to water treatment processes, when raw water is taken from wells, rivers, or lakes, the water solution is an extremely dilute liquid of mineral salts and gases. The dissolved mineral salts are a result of water flowing over and through the earth layers. The dissolved gases are atmospheric oxygen and carbon dioxide that are picked up by water-atmosphere contact. Wastewater picks up corrosive materials mainly from industrial processes and/or from chemicals added to the wastewater during treatment.

Important Point: Materials such as acids, caustic solutions, and similar solutions are typical causes of pipe corrosion.

There are several types of corrosion to be considered in water and wastewater distribution or collection piping systems:17 1. Internal corrosion — caused by aggressive water flowing through the pipes 2. External corrosion — caused by the soil’s chemical and electrical conditions 3. Bimetallic corrosion — caused when components made of dissimilar metals are connected 4. Stray-current corrosion — caused by uncontrolled DC electrical currents flowing in the soil

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8.3.6 JOINING METALLIC PIPE According to Crocker, pipe joint design and selection can have a major impact on the initial cost, long-range operating cost, and the performance of the piping system. When determining the type of joint to be used in connecting pipe, certain considerations must be made. For example, initial considerations include: material cost, installation labor cost, and degree of leakage integrity required. The operator is also concerned with periodic maintenance requirements, and specific performance requirements.18 Metallic piping can be joined or connected in a number of ways. The method used depends on: (1) the nature of the metal sections (ferrous, nonferrous) being joined, (2) the kind of liquid or gas to be carried by the system, (3) pressure and temperature in the line, and (4) access requirements.

A joint is defined simply as the connection between elements in a piping system. At present, there are five major types of joints, each used for a special purpose, used for joining metal pipe: (see Figure 8.5) 1.

2.

3.

4.

5.

Bell-and-spigot

Screwed (threaded)

Flanged

Bell-and-spigot joints Screwed or threaded joints Flanged joints Welded joints Soldered joints

Welded

8.3.6.1 Bell-and-Spigot Joints The bell-and-spigot joint has been around since its development in the late 1780s. The joint is used for connecting lengths of cast iron water and wastewater pipe (gravity flow only). The bell is the enlarged section at one end of the pipe; the plain end is the spigot (see Figure 8.5). The spigot end is placed into the bell, and the joint is sealed.

The joint sealing compound is typically made up with lead and oakum. Lead and oakum constitute the prevailing joint sealer for sanitary systems. Bell-and-spigot joints are usually reserved for sanitary sewer systems; they are no longer used in water systems.

Important Point: Bell-and-spigot joints are not used in ductile iron pipe.

8.3.6.2 Screwed or Threaded Joints Screwed or threaded joints (see Figure 8.5) are commonly used to join sections of smaller-diameter low pressure pipe; they are used in low-cost, noncritical applications such as domestic water, industrial cooling, and fire protection systems. Diameters of ferrous or nonferrous pipe joined by threading range from 1/8 to 8 in. Most couplings have threads on the inside surface. The advantages of this type of connection are its relative simplicity, ease of installation (where disassembly and reassembly are necessary Š 2003 by CRC Press LLC

Soldered FIGURE 8.5 Common pipe joints. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

to accommodate maintenance needs or process changes), and high leakage integrity at low pressure and temperature where vibration is not encountered. Screwed construction is commonly used with galvanized pipe and fittings for domestic water and drainage applications.

Important Point: Maintenance supervisors must ensure that screwed or threaded joints are used within the limitations imposed by the rules and requirements of the applicable code.

8.3.6.3 Flanged Joints As shown in Figure 8.6, flanged joints consist of two machined surfaces that are tightly bolted together with a gasket between them. The flange is a rim or ring at the end of the fitting, which mates with another section. Flanges are

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Weld metal Backing ring Butt weld FIGURE 8.6 Flanged assembly. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Socket weld FIGURE 8.8 Two kinds of welding pipe joints. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Plain faces

process whereby metal sections to be joined are heated to such a high temperature that they melt and blend together.

The advantage of welded joints is obvious: the pieces joined become one continuous piece. When a joint is properly welded, the joint is as strong as the piping.

There are two basic types of welded joints are (see Figure 8.8):

Raised faces FIGURE 8.7 Flange faces. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

joined either by being bolted together or welded together.

Some flanges have raised faces and others have plain faces, as shown in Figure 8.7. Steel flanges generally have raised faces, and iron flanges usually have plain or flat faces.

Important Point: A flange with a raised face should never be joined to one with a plain face.

Flanged joints are used extensively in water and wastewater piping systems because of their ease of assembly and disassembly, but they are expensive. Contributing to the higher cost are the material costs of the flanges and the labor costs for attaching the flanges to the pipe and then bolting the flanges each other.19 Flanged joints are not normally used for buried pipe because of their lack of flexibility to compensate for ground movement. Instead, flanged joints are primarily used in exposed locations where rigidity, self-restraint, and tightness are required (e.g., inside treatment plants and pumping stations).

1. Butt-welded joints — With these joints, the sections to be welded are placed end-to-end. This is the most common method of joining pipe used in large industrial piping systems.

2. Socket-welded joints — With these joints, one pipe fits inside the other, the weld being made on the outside of the lap. They are used in applications where leakage integrity and structural strength are important.

8.3.6.5 Soldered and Brazed Joints Soldered and brazed joints are most often used to join copper and copper-alloy (non-ferrous metals) piping systems, although brazing of steel and aluminum pipe and tubing is possible. The main difference between brazing and welding is the temperatures employed in each process.

Brazing is accomplished at far lower temperatures, but requires higher temperatures than soldering. In both brazing and soldering, the joint is cleaned (using emery cloth) and then coated with flux that prevents oxides from forming.

The clean, hot joint draws solder or brazing rod (via capillary action) into the joint to form the connection. The parent metal does not melt in brazed or soldered construction.

8.3.6.4 Welded Joints

8.4 NONMETALLIC PIPING

For applications involving high pressures and temperatures, welded joints are preferred. Welding of joints is the

Although metal piping is widely used today, nonmetallic piping (especially clay and cement) is of equal importance.

Š 2003 by CRC Press LLC

Water and Wastewater Conveyance

New processes to make them more useful in meeting today’s requirements have modified these older materials.

However, relatively speaking, using metallic piping is a new practice. All piping was originally made from clay or wood, and stone soon followed. Open stone channels or aqueducts were used to transport water over long distances. After nearly 2000 years of service, some of these open channels are still in use today.

Common practice today is to use metal piping, though nonmetallic piping is of equal importance and has many applications in water and wastewater operations. Many of the same materials that have been used for centuries (e.g., clay) are still used today, but now many new piping materials are available; the choice depends on the requirements of the planned application. The development of new technological processes has enabled the modification of older materials for new applications in modern facilities, and has brought about the use of new materials for old applications as well.

In this section, we study nonmetallic piping materials — what they are, and where they are most commonly used.

We also describe how to join sections of nonmetallic piping, and how to maintain them.

8.4.1 NONMETALLIC PIPING MATERIALS Nonmetallic piping materials used in water and wastewater applications include clay (wastewater), concrete (water and wastewater), asbestos-cement pipe (water and wastewater), and plastic (water and wastewater). Other nonmetallic piping materials include glass (chemical porcelain pipe) and wood (continuous-strip wooden pipes for carrying water and waste chemicals are used in some areas, especially in the western part of the U.S.). These materials are not discussed in this text because of their limited application in water and wastewater operations.

Important Point: As with the use of metallic piping, nonmetallic piping must be used in accordance with specifications established and codified by a number of engineering societies and standards organizations. These codes were devised to help ensure personnel safety and protection of equipment.

8.4.1.1 Clay Pipe Clay pipes are used to carry and collect industrial wastes, wastewater, and storm water (they are not typically used to carry potable water). Clay pipes typically range in size from 4 to 36 in. in diameter, and are available in various grades and strengths.

Clay pipe is used in nonpressurized systems. For example, when used in drainpipe applications, liquid flow is solely dependent on gravity; that is, it is used as an open-channel pipe, whether partially or completely filled. © 2003 by CRC Press LLC

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(A)

(B)

(C)

FIGURE 8.9 Section of bell-and-spigot fittings for clay pipe: (A) wye; (B) double wye; (C) tee. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Spigot

Bell

FIGURE 8.10 Bell and spigot ends of clay pipe sections. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Clay pipe is manufactured in two forms: vitrified (glasslike) and unglazed (not glassy) Important Point: Vitrified clay pipe is extremely corrosion proof. It is ideal for many industrial waste and wastewater applications.

Important Point: McGhee recommends that wyes and tees (see Figure 8.9) should be used for joining various sections of wastewater piping.

Failure to provide wyes and tees in common wastewater lines invites builders to break the pipe to make new connections. Obviously, this practice should be avoided, because such breaks are seldom properly sealed and can be a major source of infiltration.20 Both vitrified and unglazed clay pipe is made and joined with the same type of bell-and-spigot joint described earlier. The bell-and-spigot shape is shown in Figure 8.10.

In joining sections of clay pipe, both ends of the pipe must first be thoroughly cleaned. The small (spigot) end of the pipe must be centered properly, and then seated securely in the large (bell) end. The bell is then packed with fibrous material (usually jute) for solid joints, which is tamped down until about 30% of the space is filled. The joint is then filled with sealing compound. In flexible joint applications, the sealing elements are made from natural or synthetic rubber or a plastic-type material.

Drainage and wastewater collection lines designed for gravity flow are laid downgrade at an angle, with the bell ends of the pipe pointing upgrade. The pipe is normally placed in a trench with strong support members (along its small dimension and not on the bell end). Vitrified clay

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pipe can be placed directly into a trench and covered with soil. However, unglazed clay pipe must be protected against the effects of soil contaminants and ground moisture.

8.4.1.2 Concrete Pipe Concrete is another common pipe material, and is sometimes used for sanitary sewers in locations where grades, temperatures, and wastewater characteristics prevent corrosion.21 The pipe provides both high tensile and compressive strength and corrosion resistance.

Concrete pipe is generally found in three basic forms: (1) nonreinforced concrete pipe; (2) reinforced concrete, cylinder, and non-cylinder pipe; and (3) reinforced and prestressed concrete pressure pipe.

With the exception of reinforced and prestressed pressure pipe, most concrete pipe is limited to low-pressure applications. Moreover, almost all-concrete piping is used for conveying industrial wastes, wastewater, and storm water; similarly, some is used for water service connections.

Rubber gaskets are used to join sections of many nonreinforced concrete pipe. However, for circular concrete sewer and culvert pipe, flexible, watertight, rubber joints are used to join pipe sections.

The general advantages of concrete pipe include the following: 1. It is relatively inexpensive to manufacture.

2. It can withstand relatively high internal pressure or external load.

3. It is highly resistant to corrosion (internal and external).

4. When installed properly, it generally has a very long, trouble-free life.

5. There are minimal bedding requirements during installation.

Disadvantages of concrete pipe include: 1. It is very heavy, and thus expensive, when shipped long distances.

2. Its weight makes special handling equipment necessary.

3. The exact pipes and fittings must be laid out in advance for installation.22 8.4.1.2.1 Nonreinforced Concrete Pipe Nonreinforced concrete pipe, or ordinary concrete pipe, is manufactured in from 4- to 24-in. diameters. As in vitrified clay pipe, nonreinforced concrete pipe is made with belland-spigot ends. Nonreinforced concrete pipe is normally used for small wastewater (sewer) lines and culverts. Š 2003 by CRC Press LLC

8.4.1.2.2 Reinforced Concrete Pipe All concrete pipe made in sizes larger that 24 in. is reinforced, but reinforced pipe can also be obtained in sizes as small as 12 in. Reinforced concrete pipe is used for water conveyance (cylinder pipe), carrying wastewater, stormwater, and industrial wastes. It is also used in culverts. It is manufactured by wrapping high-tensile strength wire or rods about a steel cylinder that has been lined with cement mortar. Joints are either bell-and-spigot or tongueand groove in sizes up to 30 in., and tongue-and-groove is exclusively above that size.

8.4.1.2.3 Reinforced and Prestressed Concrete Pipe When concrete piping is to be used for heavy load highpressure applications (up to 600 psi), it is strengthened by reinforcement and prestressing. Prestressed concrete pipe is reinforced by steel wire, steel rods, or bars embedded lengthwise in the pipe wall. If wire is used, it is wound tightly to prestress the core and is covered with an outer coating of concrete. Prestressing is accomplished by manufacturing the pipe with a permanent built-in compression force.

8.4.1.2.4 Asbestos Cement Pipe Before beginning a brief discussion of asbestos-cement (A-C) pipe, it is necessary to discuss safety and health implications involved with performing maintenance activities on A-C pipe.

Prior to 1971, asbestos was known as the “material of a thousand uses.�23 It was used for fireproofing (primarily), insulation (secondarily, on furnaces, ducts, boilers and hot water pipes, for example), soundproofing, and a host of other applications, including its use in conveyance of water and wastewater. However, while still used in some industrial applications and in many water and wastewater-piping applications, asbestos containing materials (ACM), including A-C pipe, are not as widely used as they were before 1971.

Asbestos containing materials lost favor with regulators and users primarily because of the health risks involved. Asbestos has been found to cause chronic and often-fatal lung diseases, including asbestosis and certain forms of lung cancer. Although debatable, there is some evidence that asbestos fibers in water may cause intestinal cancers as well. It is true that asbestos fibers are found in some natural waters24 and can be leached from asbestos cement pipe by very aggressive waters (i.e., those that dissolve the cement25). However, it is also true that the danger from asbestos exposure is not so much due to the danger of specific products (e.g., A-C pipe) as it is to the overall exposure of people involved in the mining, production, installation, and ultimate removal and disposal of asbestos products.26 A-C pipe is composed of a mixture of Portland cement and asbestos fiber, which is built up on a rotating steel

Water and Wastewater Conveyance

mandrel and then compacted with steel pressure rollers.

This pipe has been used for over 70 years in the U.S. Because it has a very smooth inner surface, it has excellent hydraulic characteristics.27 In water and wastewater operations, it is the ultimate removal and disposal of asbestos cement pipe that poses the problem for operators. For example, consider an underground wastewater line-break that must be repaired.

After locating exactly where the line-break is (sometimes difficult to accomplish, because A-C pipe is not as easily located as conventional pipe), the work crew must first excavate the soil covering the line-break, being careful not to cause further damage since A-C pipe is relatively fragile. Once the soil has been removed, exposing the linebreak, the damaged pipe section must be removed. In some instances, it may be more economical or practical to remove the damaged portion of the pipe only, and to install a replacement portion and then girdle it with a clamping mechanism (sometimes referred to as a saddle-clamp).

To this point in the described repair operation, there is little chance for exposure to personnel from asbestos.

In order to be harmful, ACM must release fibers that can be inhaled. The asbestos in undamaged A-C pipe is not friable (nonfriable asbestos); it cannot be readily reduced to powder form by hand pressure when it is dry. Thus, it poses little or no hazard in this condition. However, if the maintenance crew making the pipe repair must cut, grind, or sand the A-C pipe section under repair, the non-friable asbestos is separated from its bond. This type of repair activity is capable of releasing friable airborne fibers — this is the hazard of working with A-C pipe.

To guard against the hazard of exposure to asbestos fibers, A-C pipe repairs must be accomplished in a safe manner. Operators must avoid any contact with ACM that disturbs its position or arrangement, disturbs its matrix or renders it friable, and generates any visible debris from it.

Important Point: Visibly damaged, degraded, or friable ACM in the vicinity are always indicators that surface debris or dust could be contaminated with asbestos. Occupational Health and Safety Administration standards require that we assume that such dust or debris contains asbestos fibers.28 In the A-C pipe repair operation described above, repairs to the A-C pipe require that prescribed U.S. Environmental Protection Agency (EPA), Occupational Health and Safety Administration (OSHA), state, and local guidelines be followed. General EPA/OSHA guidelines, at a minimum, require that trained personnel perform repairs made to the A-C pipe, only. The following safe work practice is provided for those who must work on or with ACM (i.e., A-C pipe). Š 2003 by CRC Press LLC

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8.4.1.2.4.1

Safe Work Practice: A-C Pipe29

1. When repairs/modifications are conducted that require cutting, sanding, or grinding on cement pipe containing asbestos, EPA-trained asbestos workers or supervisors are to be called to the work site immediately.

2. Excavation personnel will unearth buried pipe to the point necessary to make repairs or modifications. The immediate work area will then be cleared of personnel as directed by the asbestos-trained supervisor.

3. The on-scene supervisor will direct the asbestostrained workers as required to accomplish the work task.

4. The work area will be barricaded 20 ft in all directions to prevent unauthorized personnel from entering.

5. Asbestos-trained personnel will wear all required Personal Protective Equipment (PPE).

Required PPE shall include Tyvek totally enclosed suits, 1/2 face respirator equipped with HEPA filters, rubber boots, goggles, gloves, and hard hats.

6. Supervisor will perform the required air sampling before entry.

7. Air sampling shall be conducted using National Institute for Occupational Safety and Health (NIOSH) 7400 Protocol.

8. A portable decontamination station will be set up as directed by supervisor.

9. Workers will enter the restricted area only when directed by the supervisors and, using wet methods only, will either perform pipe cutting using a rotary cutter assembly or inspect the broken area to be covered with repair saddle device.

10. After performing the required repair or modifications, workers will encapsulate bitter ends and fragmented sections.

11. After encapsulation, the supervisor can authorize entry into restricted area for other personnel.

12. Broken ACM pipe pieces must be properly disposed of following EPA, state, and local guidelines.

Important Point: Although exposure to asbestos fibers is dangerous, it is important to note that studies

by EPA, AWWA, and other groups have concluded that the asbestos in water mains does not generally constitute a health threat to the public.30 Because A-C pipe is strong and corrosion resistant, it is widely used for carrying water and wastewater. Standard sizes range from 3 to 36 in. Though highly resistant to corrosion, A-C pipe should not be used for carrying highly acid solutions or unusually soft water, unless its inner and

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outer surface walls are specially treated. A-C pipe is preferred for use in many outlying areas because of its light weight, which results in greater ease of handling.

Using an asbestos-cement sleeve joins A-C pipe. The sleeve’s I.D. is larger than the pipe’s O.D. The ends of the pipes fit snugly into the sleeve and are sealed with a natural or synthetic rubber seal or gasket, which acts as an expansion joint.

8.4.1.3 Plastic Pipe Plastic pipe has been used in the U.S. for about 60 years; its use is becoming increasingly common. In fact, because of its particular advantages, plastic pipe is replacing both metallic and nonmetallic piping. The advantages of plastic piping include: 1.

2.

3.

4.

5.

6.

7.

8.

9.

Internal and external high corrosion resistance Rarely needs to be insulated or painted Lightweight Ease of joining Freedom from rot and rust Will not burn (readily) Lower cost Long service life Easy to maintain

There are several types of plastic pipe. Plastic pipe is commonly used in water and wastewater service, but PVC is the most common plastic pipe for municipal water distribution systems.

PVC is a polymer extruded (shaped by forcing through a die) under heat and pressure into a thermoplastic that is nearly inert when exposed to most acids, fuels, and corrosives. PVC is commonly used to carry cold drinking water, because it is nontoxic and will not affect the water’s taste or cause odor.

The limitations of PVC pipe include its limited temperature range (approximately 150 to 250∞ F) and lowpressure capability (usually 75 to 100 psi).

Joining sections of plastic pipe is accomplished by welding (solvent, fusion, fillet), threading, and flanges.

Important Point: The strength of plastic piping decreases as the temperature of the materials it carries increases.

8.5 TUBING Piping by Another Name Might be Tubing?

A logical question might be, when is a pipe a tube, or a tube a pipe?. Does it really matter if we call piping or tubing by two distinct, separate, and different names? It depends, of course, on the differences between the two. © 2003 by CRC Press LLC

When we think of piping and tubing, we think of tubular, which infers cylindrical products that are hollow.

Does this description help us determine the difference between piping and tubing? No, not really. We need more — a more concise description or delineation.

Maybe size will work. It is true that when we normally think of pipe, we think in terms of either metallic or nonmetallic cylindrical products that are hollow and range in nominal size from about 0.5 inch (or less) to several feet in diameter. On the other hand, when we think of tubing we think of cylindrical, hollow products that are relatively smaller in diameter than that of many piping materials.

Maybe application will work. It is true that when we normally think of pipe, we think of any number of possible applications from conveying raw petroleum from field to refinery, to the conveyance of raw water from source to treatment facility, to wastewater discharge point to treatment to outfall, and several others. When we think in terms of tubing applications and products conveyed, the conveyance of compressed air, gases (including liquefied gas), steam, water, lubricating oil, fuel oil, chemicals, fluids in hydraulic systems, and waste products comes to mind.

On the surface, and evidenced by the discussion above, it is apparent that when we attempt to classify or differentiate piping and tubing, our effort is best characterized as somewhat arbitrary, capricious, vague, and ambiguous. It appears that piping by any other name is just piping. In reality, piping is not tubing, and in the end (so to speak) the difference may come down to determination by end use.

The bottom line is that it is important to differentiate between piping and tubing because they are different.

They are different in physical characteristics and methods of installation, as well as in their advantages and disadvantages. In this chapter, these differences become clear.

8.5.1 TUBING

VS.

PIPING: THE DIFFERENCE

Lohmeier and Avery point out that piping and tubing are considered separate products, even though they are geometrically quite similar. Moreover, the classification of pipe or tube is determined by end use.31 As mentioned, many of the differences between piping and tubing are related to physical characteristics, methods of installation, and the advantages and disadvantages.

8.5.1.1 Tubing Simply, tubing refers to tubular materials (products) made to either an I.D. or O.D. (expressed in even inches or fractions). Tubing walls are generally much thinner than those of piping; thus, wall thickness in tubing is of particular importance.

Important Point: Wall thickness tolerance in tubing is held so closely that wall thickness is usually

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given in thousandths of an inch rather than as a fraction of an inch. Sometimes a gauge number is used to indicate the thickness according to a given system.

Tubing of different diameters has different wall thickness. An example from “Pipe Properties” and “Tubing Properties” illustrates the difference between piping and tubing.32 The wall thickness of a commercial type of 8-in. pipe is 0.406 in. Light-wall 8-in. copper tubing, by contrast, has a wall thickness of 0.050 in. When we compare these figures, it is clear that tubing has much thinner walls than piping of the same general diameter.

Important Note: It is important to note that the range between thick and thin is narrower for tubing than it is for piping.

The list of tubing applications is a lengthy one. Some tubing types can be used not only as conduits for electrical wire, but also used to convey waste products, compressed air, hydraulic fluids, gases, fuel oil, chemicals, lubricating oil, stream, waters, and other fluids (i.e., both gaseous and liquid).

Tubing is made from both metals and plastics. Metal tubing is designed to be somewhat flexible but also strong.

Metallic materials such as copper, aluminum, steel, and stainless steel are used in applications where fluids are carried under high pressure (some types of tubing [e.g., stainless steel] can accommodate very high pressures [>5000 psi]). As the diameter of the tubing increases, the wall thickness increases accordingly (slightly).

Ranging in size from 1/32 to 12 in. in diameter, it is the smaller sizes that are most commonly used. Standard copper tubing ranges from 1/32 to 10 in. in diameter, steel ranges from 3/15 in. to 10¾ in., aluminum ranges from 1/8 to 12 in., and special alloy tubing is available up to 8 in. in diameter.

One of the primary reasons tubing is employed for industrial applications is the fact that some tubing materials are extremely resistant to deterioration by corrosive chemicals.

Typically, in terms of initial cost, metal tubing materials are more expensive than iron piping. However, high initial cost vs. ability to do a particular application as designed (or desired), is a consideration that cannot be overlooked or underemphasized. Consider, for example, an air compressor. Typically, while in operation, air compressors are mechanical devices that not only produce a lot of noise, but also vibrate. Installing a standard rigid metal piping system to such a device might not be practical. Installing tubing that is flexible to the same device, however, may have no detrimental impact on operation whatsoever. An even more telling example is the internal combustion engine. For example, a lawnmower engine, like the air compressor, also vibrates and is used in less © 2003 by CRC Press LLC

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than static conditions (i.e., the lawnmower is typically exposed to all kinds of various dynamic stresses). Obviously, we would not want the fuel lines (tubing) in such a device to be hard-wired with rigid pipe; instead, we would want the fuel lines to be durable but also somewhat flexible. Thus, flexible metal tubing is called for in this application because it will hold up.

Simply put, initial cost can be important. However, considerations such as maintenance requirements, durability, length of life, and ease of installation, often favor the use of metallic tubing over the use of metallic pipe.

While it is true that most metallic tubing materials have relatively thin walls, it is also true that most are quite strong. Small tubing material with thin walls (i.e., soft materials up to approximately 1 in. O.D.) can be bent quite easily by hand. Tubing with larger diameters requires special bending tools. The big advantage of flexible tubing should be obvious: tubing can be run from one point to another with fewer fittings than if piping was used.

Note: Figure 8.11 shows how the use of tubing can eliminate several pipefittings.

The advantages of the tubing type of arrangement shown in Figure 8.11 include the following: 1. It eliminates eighteen potential sources of leaks.

2. The cost of the 18 90∞ elbow fittings needed for the piping installation is eliminated.

3. The time needed to cut, gasket, and flange the separate sections of pipe is conserved. (It takes little time to bend tubing into the desired configuration.)

4. A tubing configuration is much lighter in weight than the separate lengths of pipe and the pipe flanges would have been.

As mentioned, in the configuration shown in Figure 8.11, the amount of weight is considerably less for the copper tubing than the piping arrangement. Moreover, the single length of tubing bent to follow the same general conveyance route is much easier to install.

It may seem apparent to some readers that many of the weight and handling advantages of tubing compared to piping can be eliminated or at least matched simply by reducing the wall thickness of the piping. It is important to remember, that piping has a thick wall because it often needs to be threaded to make connections. For example if the wall thickness of iron pipe was made comparable to the thickness of copper tubing and then threaded at connection points, its mechanical integrity would be reduced. The point is piping must have sufficient wall thickness left after threading to not only provide a tight fit, but also to handle the fluid pressure. On the other hand, copper tubing is typically designed for brazed and soldered connections, rather than threaded ones. Thus, its

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Piping and fittings

Tubing

FIGURE 8.11 Tubing eliminates fittings. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

8.5.2.1 Tubing: Mechanical Advantages

Threaded pipe section

Pipe section without threads FIGURE 8.12 Pipe wall thickness is important when threading is required. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

wall thickness can be made uniformly thin. This advantage of tubing over iron piping is illustrated in Figure 8.12.

Important Point: The lighter weight of tubing means greater ease of handling, as well as lower shipping costs.

8.5.2 ADVANTAGES

OF

TUBING

To this point, in regards to design requirements, reliability, and maintenance activities of using tubing instead of piping, we have pointed out several advantages of tubing.

These advantages can be classified as mechanical and chemical advantages. Š 2003 by CRC Press LLC

Probably the major mechanical advantage of using tubing is its relatively small diameter and its flexibility. These features make it user-friendly in tight spaces where piping would be difficult to install and to maintain (i.e., for the tightening or repair or replacement of fittings).

Another mechanical advantage of tubing important to water and wastewater maintenance operators is the ability of tubing to absorb shock from water hammer. Water hammer can occur whenever fluid flow is started or stopped. In water and wastewater operations, certain fluid flow lines have a frequent on-off cycle. In a conventional piping system, this may produce vibration, which is transmitted along the rigid conduit, shaking joints, valves, and other fittings. The resulting damage usually results in leaks that need repairs. In addition, the piping supports can also be damaged. When tubing, with its built-in flexibility, is used in place of conventional iron piping, the conduit absorbs most of the vibration and shock. The result is far less wear and tear on the fittings and other appurtenances.

As mentioned, sections of tubing are typically connected by means of soldering, brazing, or welding rather than by threaded joints. However, steel tubing is sometimes joined by threading. In addition to the advantages in cost and saving time, avoidance of using threaded joints precludes other problems. For example, any time piping is threaded it is weakened. At the same time, threading is commonly used for most piping systems and usually presents no problem.

Another advantage of tubing over iron piping is the difference in inner-wall surfaces between the two. Specifically, tubing generally has a smoother inner-wall surface than iron piping. This smoother inner-wall characteristic

Water and Wastewater Conveyance

aids in reducing turbulent flow (wasted energy and decreased pressure) in tubing. Instead, flow in the smoother walled tubing is more laminar; it has less turbulence. Laminar flow is characterized as flow in layers — very thin layers. (Somewhat structurally analogous to this liquid laminar flow phenomenon is wood type products such as kitchen cabinets. Many of these are constructed of laminated materials.)

This might be a good time to address laminar flow inside a section of tubing. First, we need to discuss both laminar and turbulent flow in order to point out the distinct difference between them. Simply, in laminar flow, streamlines remain parallel to one another and no mixing occurs between adjacent layers. In turbulent flow, mixing occurs across the pipe. The distinction between the two regimes lies in the fact that the shear stress in laminar flow results from viscosity. In turbulent flow the shear stress results from momentum exchanges occurring as a result of motion of fluid particles from one layer to another.33 Normally flow is laminar inside tubing. If there are irregularities (dents, scratches, or bumps) on the tubing’s inner wall, the fluid will be forced across the otherwise smooth surface at a different velocity. This causes turbulence.

In contrast to tubing, iron piping has more irregularities along its inner walls. This inner-wall surface roughness produces turbulence in the fluid flowing along the conduit.

Ultimately, this turbulence can reduce delivery rate of the piping system considerably.

8.5.2.2 Chemical Advantages The major chemical advantage in tubing as compared to piping comes from the corrosion-resistant properties of the metals used to make the tubing. Against some corrosive fluids, most tubing materials do very well. Some metals perform better than others, depending upon the metal and the corrosive nature of the fluid.

It is important to also point out that tubing used must be compatible with the fluid being conveyed. When conveying a liquid stream from one point to another, the last thing wanted is contamination from the tubing to be added to the fluid. Many tubing conveyance systems are designed for use in food-processing operations, for example. If we were conveying raw milk to or from a unit process, we certainly would not want to contaminate the milk. To avoid such contamination, where conditions of particular sanitation are necessary, stainless steel, aluminum, or appropriate plastic tubing must be used.

8.5.3 CONNECTING TUBING The skill required to properly connect metal or nonmetallic tubing can be learned by just about anyone. A certain amount of practice and experience is required to ensure the tubing is properly connected. Moreover, certain tools © 2003 by CRC Press LLC

255

are required for connecting sections of tubing. The tools used to make either a soldered connection or a compression connection (where joint sections are pressed together) include: 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Hacksaw Tube cutter Scraper Flat file Burring tool Flaring tool Presetting tool for flareless fittings Assorted wrenches Hammer Tube bender

8.5.3.1 Cutting Tubing No matter what type of connection you are making (soldered or compressed), it is important to cut the tubing cleanly and squarely. This can be accomplished using a tubing cutter. Use of a tubing cutter is recommended because it provides a much smoother cut than that made with a hacksaw. A typical tubing cutter has a pair of rollers on one side and a cutting wheel on the other. The tubing cutter is turned all the way around the tubing, making a clean cut.

Important Point: When cutting stainless steel tubing, cut the tubing as rapidly and safely as you can, with as few strokes as possible. This is necessary because as stainless steel is cut, it hardens, especially when cut with a hacksaw.

After making the tubing cut, the rough edge of the cut must be smoothed with a burring tool to remove the small metal chads, burrs, or whiskers. If a hacksaw is used to cut the tubing, ensure that the rough cut is filed until it is straight and square to the length of tubing.

8.5.3.2 Soldering Tubing34 Soldering is a form of brazing in which nonferrous filler metals having melting temperatures below 800∞F (427°C) are used. The filler metal is called solder (usually a tin-lead alloy, which has a low melting point) and is distributed between surfaces by capillary action.

Whether soldering two sections of tubing together or connecting tubing to a fitting, such as an elbow, the soldering operation is the same. Using emery cloth or a wire brush, the two pieces to be soldered must first be cleaned (turned to bright metal). Clean, oxide-free surfaces are necessary to make sound soldered joints. Uniform capillary action is possible only when surfaces are completely free of foreign substances such as dirt, oil, grease, and oxide.

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Important Point: During the cleaning process care must be taken to avoid getting the prepared adjoining surfaces too smooth. Surfaces that are too smooth will prevent the filler metal (solder) from effectively wetting the joining areas.

The next step is to ensure that both the tubing outside and the fitting inside are covered with soldering flux and fitted together. When joining two tubing ends, use a sleeve.

The purpose of flux is to prevent or inhibit the formation of oxide during the soldering process. The two ends are fitted into the sleeve from opposite sides. Make sure the fit is snug.

Next, heat the joint. First, heat the tubing next to the fitting then the fitting itself. When the flux beings to spread, solder should be added (this is known as tinning).

The heat will suck the solder into the space between the tubing and the sleeve. Then heat the fitting, on an off, and apply more solder until the joint is fully penetrated.

Important Point: During the soldering operation, it is important to ensure that the heat is applied evenly around the tubing. A continuous line of solder will appear where the fitting and tubing meet at each end of the sleeve. Also, ensure that the joined parts are held so that they will not move. After soldering the connection, wash the connection with hot water to prevent future corrosion.

The heat source normally used to solder is heated using an oxyacetylene torch or some other high-temperature heat source.

When soldering it is important to remember the following points:

Toe of sleeve

Outside diameter of sleeve Flare

Sleeve

FIGURE 8.13 Flared tubing end. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Male connect body

Nut

Sleeve support tube

Tube Flare

FIGURE 8.14 Flared fitting. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Bite

Ferrule

Pipe thread

Tube Body Nut

1. Always use the recommended flux when soldering.

2. Make sure parts to be soldered are clean and their surfaces fit closely together.

3. During the soldering process do not allow the parts to move while the solder is in a liquid state.

4. Be sure the soldering heat is adequate for the soldering job to be done, including the types of metal and the fluxes.

5. Wash the solder work in hot water to stop later corrosive action.

8.5.3.3 Connecting Flared/Nonflared Joints In addition to being connected by brazing or soldering, tubing can also be connected by either flared or nonflared joints. Flaring is accomplished by evenly spreading the end of the tube outward, as shown in Figure 8.13. The accuracy of the angle of flare is important; it must match the angle of the fitting being connected. The flaring tool Š 2003 by CRC Press LLC

FIGURE 8.15 Flareless fitting. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

is inserted into the squared end of the tubing, and then hammered or impacted into the tube a short distance, spreading the tubing end as required.

8.5.3.3.1 Flared Connection Figure 8.14 shows the resulting flared connection. The flared section is inserted into the fitting in such a way that the flared edge of the tube rests against the angled face of the male connector body — a sleeve supports the tubing.

The nut is tightened firmly on the male connector body, making a firm joint that will not leak, even if the tubing ruptures because of excess pressure.

8.5.3.3.2 Nonflared Connection Figure 8.15 shows a flareless fitting. As shown, the plain tube end is inserted into the body of the fitting. Notice that there are two threaded outer sections with a ferrule

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Correct

Flat

Kinked

Wrinkled

Incorrect FIGURE 8.16 Correct and incorrect tubing bends. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

or bushing located between them. As the threaded members are tightened, the ferrule bites into the tubing, making a tight connection.

8.5.4 BENDING TUBING A type of tool typically used in water and wastewater maintenance applications for bending tubing is the hand bender. This is nothing more than a specifically sizedspring-type apparatus. Spring-type benders come in several different sizes (the size that fits the particular sized tubing to be bent is used to bend it). The spring-type tubing bender is slipped over the tubing section to be bent. Then, carefully, the spring and tubing are bent by hand to conform to the angle of bend desired.

In using any type of tubing bender, it is important to obtain the desired bend without damaging (flattening, kinking, or wrinkling) the tubing. As mentioned, any distortion of the smooth, inner wall of a tubing section causes turbulence in the flow, which lowers the pressure.

Figure 8.16 shows three different kinds of incorrect bends and one correct bend. From the figure, it should be apparent how the incorrect bends constrict the flow, causing turbulence and lower pressure.

8.5.5 TYPES

OF

TUBING

Common types of metal tubing in industrial service include: 1. Copper (seamless, fully annealed, furnished in coils or in straight lengths) — In water treatment applications, copper tubing has replaced lead and galvanized iron in service line instalŠ 2003 by CRC Press LLC

lations because it is flexible, easy to install, corrosion resistant in most soils, and able to withstand high pressure. It is not sufficiently soluble in most water to be a health hazard, but corrosive water may dissolve enough copper to cause green stains on plumbing fixtures. Copper water service tubing is usually connected by either flare or compression fittings. Copper plumbing is usually connected with solder joints.35 Important Point: Annealing is the process of reheating a metal and then letting it cool slowly. In the production of tubing, annealing is performed to make the tubing softer and less brittle.

2. Aluminum (seamless, annealed, and suitable for bending and flaring) 3. Steel (seamless, fully annealed, also available as a welded type, suitable for bending and flaring) 4. Stainless steel (seamless, fully annealed, also available as a welded type, suitable for bending and flaring) 5. Special alloy (made for carrying corrosive materials).

Like metal piping, metal tubing is made in both welded and seamless styles. Welded tubing begins as flat strips of metal that is then rolled and formed into tubing.

The seam is then welded.

Seamless tubing is formed as a long, hot metal ingot and then shaped into a cylindrical shape. The cylinder is then extruded (passed through a die), producing tubing in

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the larger sizes and wall thicknesses. If smaller tubing (with thinner walls and closer tolerances) is desired, the extruded tubing is reworked by drawing it through another die.

8.5.5.1 Typical Tubing Applications In a typical water or wastewater operation, tubing is used in unit processes and machinery. Heavy-duty tubing is used for carrying gas, oxygen, steam, and oil in many underground services, interior plumbing, and heating and cooling systems throughout the plant site. Steel tubing is used in high-pressure hydraulic systems. Stainless steel tubing is used in many of their chemical systems. In addition, in many plants, aluminum tubing is used as raceways or containers for electrical wires.

Plastics have become very important as nonmetallic tubing materials. The four most common types of plastic tubing are Plexiglas (acrylic), polycarbonate, vinyl, and polyethylene.

For plant operations, plastic tubing usage is most prevalent where it meets corrosion resistance demands, and the temperatures are within its working range. It is primarily used in chemical processes.

Plastic tubing is connected either by fusing with solvent-cement or by heating. Reducing the plastic ends of the tubing to a soft, molten state, then pressing them together, makes fused joints. In the solvent-cement method, the ends of the tubing are coated with a solvent that dissolves the plastic. The tube ends are firmly pressed together, and as the plastic hardens, they are securely joined. When heat fused, the tubes are held against a hot plate. When molten, the ends are joined and the operation is complete.

8.6 INDUSTRIAL HOSES Earlier we described the uses and merits of piping and tubing. This section describes industrial hoses, which are classified as a slightly different tubular product. Their basic function is the same — to carry fluids (liquids and gases) from one point to another.

The outstanding feature of industrial hose is its flexibility, which allows it to be used in application where vibrations would make the use of rigid pipe impossible.

Most water and wastewater treatment plants use industrial hoses to convey steam, water, air, and hydraulic fluids over short distances. It is important to point out that each application must be analyzed individually, and an industrial hose must be selected which is compatible with the system specification.

In this section, we study industrial hoses — what they are, how they are classified and constructed, and the ways in which sections of hose are connected to one another and to piping or tubing. We will also examine the main-

Š 2003 by CRC Press LLC

tenance requirements of industrial hoses, and what to look for when we make routine inspections or checks for specific problems.

Industrial hoses, piping, and tubing all are used to convey a variety of materials under a variety of circumstances. Beyond this similar ability to convey a variety of materials, there are differences between industrial hoses and piping and tubing. For example, in their construction and in their advantages, industrial hoses are different from piping and tubing. As mentioned, the outstanding advantage of hose is its flexibility; its ability to bend means that hose can meet the requirements of numerous applications that cannot be met by rigid piping and some tubing systems.

Two examples of this flexibility are Camel hose (used in wastewater collection systems to clean out interceptor lines and to remove liquid from excavations where broken lines are in need of repair) and the hose that supplies hydraulic fluids used on many forklifts. Clearly, rigid piping would be impractical to use in both situations.

Industrial hose is not only flexible, but also has a dampening effect on vibration. Certain tools used in water and wastewater maintenance activities must vibrate to do their jobs. Probably the best and most familiar such tool is the power hammer, or jackhammer. Obviously, the builtin rigidity of piping and tubing would not allow vibrating tools to stand up very long under such conditions. Other commonly used tools and machines in water and wastewater operations have pneumatically or hydraulically driven components. Many of these devices are equipped with moving members that require the air or oil supply to move with them. In such circumstances, of course, rigid piping could not be used.

It is important to note that the flexibility of industrial hose is not the only consideration that must be taken to account when selecting hose over either piping or tubing.

The hose must be selected according to the potential damaging conditions of an application. These conditions include the effects of pressure, temperature, and corrosion.

Hose applications range from the lightweight ventilating hose (commonly called elephant trunk) used to supply fresh air to maintenance operators working in manholes, vaults, or other tight places. In water and wastewater treatment plants, hoses are used to carry water, steam, corrosive chemicals and gases, and hydraulic fluids under high pressure. To meet such service requirements, hoses are manufactured from a number of different materials.

8.6.1 HOSE NOMENCLATURE To gain a fuller understanding of industrial hoses and their applications, it is important to be familiar with the nomenclature or terminology normally associated with industrial hoses. Accordingly, in this section, we explain hose terminology with which water and wastewater operators should be familiar.

Water and Wastewater Conveyance

Carcass

Cover

259

Wall thickness

I.D.

O.D.

Reinforcing braid Overall length

Tube

FIGURE 8.17 Common hose nomenclature. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Figure 8.17 is a cutaway view of a high-pressure air hose of the kind that supplies portable air hammers and drills and other pneumatic tools commonly used in water and wastewater maintenance operations. The hose is the most common type of reinforced nonmetallic hose in general use. Many of the terms given have already been mentioned. The I.D., which designates the hose size, refers to the inside diameter throughout the length of the hose body, unless the hose has enlarged ends. The O.D. is the diameter of the outside wall of the hose.

As shown in Figure 8.17, the tube is the inner section (i.e., the core) of the hose, through which the fluid flows.

Surrounding the tube is the reinforcement material, which provides resistance to pressure from the inside or outside.

Notice that the hose shown in Figure 8.17 has two layers of reinforcement braid. (This braid is fashioned from high-strength synthetic cord.) The hose is said to be mandrel-braided, because a spindle or core (the mandrel) is inserted into the tube before the reinforcing materials are added. The mandrel provides a firm foundation over which the cords are evenly and tightly braided. The cover of the hose is an outer, protective covering. The hose in Figure 8.17 has a cover of tough, abrasion-resistant material.

Important Point: If the ends of an industrial hose are enlarged, as shown in Figure 8.18, the letters E.E. are used (meaning expanded or enlarged end). Some hoses have enlarged ends to fit a fixed end of piping tightly (e.g., an automobile engine).

The overall length is the true length of a straight piece of hose. The hose, which is not too flexible, is formed or molded in a curve (e.g., automobile hose used in heating systems; see Figure 8.19). As shown in Figure 8.19, the arm is the section of a curved hose that extends from the end of the hose to the nearest centerline intersection. The body is the middle section or sections of the curved hose.

Figure 8.20 shows the bend radius (i.e., is the radius of the bend measured to the centerline) of the curved hose, and designated as the radius r. In a straight hose, bent on

Š 2003 by CRC Press LLC

FIGURE 8.18 Expanded end hose. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Body

R Arm

FIGURE 8.19 Bend radius. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

R r

R = Bend radius for curved hose r = Bend radius for straight hose

FIGURE 8.20 Bend radius measurement. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

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the job, the radius of the bend is measured to the surface of the hose (i.e., radius r in Figure 8.20).

Important Point: Much of the nomenclature used above does not apply to non-metallic hose that is not reinforced. However, nonreinforced nonmetallic hose is not very common in water and wastewater treatment plant operations.

8.6.2 FACTORS GOVERNING HOSE SELECTION The amount of pressure that a hose will be required to convey is one of the important factors governing hose selection. Typically, pressure range falls in any of three general groups: 1. <250 psi (low pressure applications) 2. 250 to 3000 psi (medium pressure applications) 3. 3000 to 6000+ psi (high pressure applications) Important Point: Note that some manufacturers have their own distinct hose pressure rating scheme; we cannot assume that a hose rated as lowpressure hose will automatically be useful at 100 or 200 psi. It may, in fact, be built for pressures not to exceed 50 psi, for example.

Therefore, whenever we replace a particular hose, we must ensure that the same type of hose with the same pressure rating as the original hose is used. In high-pressure applications, this precaution is of particular importance.

In addition to the pressure rating of a hose, we must also consider, for some applications, the vacuum rating of a hose. Vacuum rating refers to suction hose applications, in which the pressure outside the hose is greater than the pressure inside the hose. It is important to know the degree of vacuum that can be created before a hose begins to collapse. A drinking straw, for example, collapses rather easily if too much vacuum is applied. Thus, it has a low vacuum rating. In contrast, the lower automobile radiator hose (also works under vacuum) has a relatively higher vacuum rating.

8.6.3 STANDARDS, CODES,

AND

SIZES

Just as they have for piping and tubing, authoritative standards organizations have devised standards and codes for hoses.

Standards and codes are safety measures designed to protect personnel and equipment. For example, specifications are provided for working pressures, sizes, and material requirements. The working pressure of a hose, for example, is typically limited to 1/4, or 25%, of the amount of pressure needed to burst the hose. For example, if we have a hose that has a maximum rated working pressure Š 2003 by CRC Press LLC

of 200 psi, it should not rupture until 800 psi has been reached, and possibly not even then. Thus, the use of hoses that meet specified standards or codes is quite evident.

8.6.3.1 Hose Size The parameter typically used to designate hose size is its I.D. In regards to classification of a hose, ordinarily a dash numbering system is used. Current practice by most manufacturers is to use the dash system to identify both hose and fittings. In determining the size of a hose, we simply convert the size to 16ths. For example, a hose size of 1/2 in. (a hose with a 1/2-in. I.D.) is the same as 8/16 in.

The numerator of the faction (the top number, or 8 in this case) is the dash size of the hose. In the same way, a 1½-in. size can be converted to 24/16 in. and so is identified as a -24 (pronounced dash 24) hose. By using the dash system, we can match a hose line to tubing or piping section and be sure the I.D. of both will be the same. This means that the non-turbulent flow of fluid will not be interrupted.

Based on I.D., hoses range in size from 3/16 in. to as large as 24 in.

8.6.4 HOSE CLASSIFICATIONS There are a number of ways in which a hose is classified.

For example, hoses can be classified by type of service (hydraulic, pneumatic, corrosion-resistant), material, pressure, and type of construction. Hoses may also be classified by type. The three types include metallic, nonmetallic, and reinforced nonmetallic. Generally, terminology is the same for each type.

8.6.4.1 Nonmetallic Hoses Relatively speaking, the use of hoses is not a recent development. Hoses, in fact, have been used for one application or another for hundreds of years. Approximately 100 years ago, after new developments in the processing of rubber, layering rubber around mandrels usually made hoses.

Later, the mandrel was removed, leaving a flexible rubber hose. These flexible hoses tended to collapse easily. Even so, they were an improvement over the earlier types. Manufacturers later added layers of rubberized canvas. This improvement gave hoses more strength, and gave them the ability to handle higher pressures. Later, after the development of synthetic materials, manufacturers had more rugged and more corrosion-resistant rubber-type materials to work with. Today, neoprene, nitrile rubber, and butyl rubber are commonly used in hoses.

However, current manufacturing practice is not to make hoses from a single material. Instead, different materials form layers in the hose, reinforcing it in various ways for strength and resistance to pressure. Hoses manufactured today usually have a rubber-type inner tube or a synthetic (e.g., plastic) lining surrounded by a carcass

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FIGURE 8.21 Vertical braided. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

(usually braided) and cover, as we saw in Figure 8.17. The type of carcass braiding used is determined by the requirements of the application.

To reinforce a hose, two types of braiding are used: vertical braiding and horizontal braiding. Vertical braiding strengthens the hose against pressure applied at right angles to the centerline of the hose. Horizontal braiding strengthens the hose along its length, giving it greater resistance to expansion and contraction.

261

FIGURE 8.22 Wrapped hose. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

FIGURE 8.23 Wire-reinforced hose. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

8.6.4.1.1 Types of Nonmetallic Hoses Descriptions of the types of nonmetallic hose follow, with references to their general applications.

8.6.4.1.1.1

Vertical-Braided Hoses

The vertical-braided hose has an inner tube of seamless rubber (see Figure 8.21). The reinforcing wrapping (carcass) around the tube is made of one or more layers of braided yarn. This type of hose is usually made in lengths of up to 100 ft with I.D.s of up to 1.5 in. Considered a small hose, it is used in low-pressure applications to carry fuel oil, acetylene gas, and oxygen for welding, and for watering lawns, gardens, and for other household uses. It is also used for spraying paint.

8.6.4.1.1.2

Horizontal-Braided Hoses

The horizontal-braided hose is mandrel built; it is used to make hose with an I.D. of up to 3 in. Used in high-pressure applications, the seamless rubber tube is reinforced by one or more layers of braided fibers or wire. This hose is used to carry propane and butane gas and steam, and is used for various hydraulic applications that require high working pressures.

8.6.4.1.1.3

Reinforced Horizontal Braided-Wire Hoses

In this type of hose, the carcasses around the seamless tube are made up of two or more layers of fiber braid with steel wire reinforcement between them. The I.D. may be up to 4 in. Mechanically very strong, this hose is used where there are high working pressures and strong suction (vacuum) forces, such as in chemical transfer and petroleum applications.

8.6.4.1.1.4

Wrapped Hoses

Made in diameters up to 24 in., the wrapped hose is primarily used for pressure service rather than suction.

The hose is constructed of mandrels, and to close tolerances (see Figure 8.22). It also has a smooth bore that Š 2003 by CRC Press LLC

FIGURE 8.24 Wire-woven hose. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

encourages laminar flow and avoids turbulence. Several plies (layers) of woven cotton or synthetic fabric make up the reinforcement. Selected for their resistance to corrosive fluids, the tube is made from a number of synthetic rubbers. It is also used in sandblasting applications.

8.6.4.1.1.5

Wire-Reinforced Hoses

In this type of hose, wires wound in a spiral around the tube, or inside the carcass, in addition to a number of layers of wrapped fabrics, provide the reinforcement (see Figure 8.23). With I.D.s of 16 to 24 in. common, this type of hose is used in oil-suction and discharge situations that require special hose ends, maximum suction (without collapsing), special flexing characteristics (must be able to bend in a small radius without collapsing), or a combination of these three requirements.

8.6.4.1.1.6

Wire-Woven Hoses

The wire-woven hose (see Figure 8.24) has cords interwoven with wire running spirally around the tube, and is highly flexible, low in weight, and resistant to collapse even under suction conditions. This kind of hose is well suited for such negative pressure applications.

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Other Types of Nonmetallic Hoses

Hoses are also made of other nonmetallic materials, many of them nonreinforced. For example, materials like Teflon®, Dacron®, polyethylene, and nylon have been developed. Dacron remains flexible at very low temperatures, even as lows as –200+∞C (up to –350∞F), nearly the temperature of liquid nitrogen. Consequently, these hoses are used to carry liquefied gas in cryogenic applications.

Where corrosive fluids and fluids up to 230+∞C (up to 450∞F) are to be carried, Teflon is often used. Teflon can also be used at temperatures as low as –55∞C (–65∞F).

Usually sheathed in a flexible, braided metal covering, Teflon hoses are well protected against abrasion; they also have added resistance to pressure.

Nylon hoses (small diameter) are commonly used as air hoses, supplying compressed air to small pneumatic tools. The large plastic hoses (up to 24 in.) we use to ventilate manholes are made of such neoprene-coated materials as nylon fabric, glass fabric, and cotton duck.

The cotton duck variety is for light-duty applications. The glass fabric type is used with portable heaters and for other applications involving hot air and fumes.

Various hoses made from natural latex, silicone rubber, and pure gum are available. The pure gum hose will safely carry acids, chemicals, and gases. Small hoses of natural latex, which can be sterilized, are used in hospitals; with pharmaceuticals, blood, and intravenous solutions; and in food-handling operations and laboratories. Silicone rubber hose is used in situations where extreme temperatures and chemical reactions are possible. It is also used as for aircraft starters, to which it provides compressed air in very large volumes. Silicone rubber hose works successfully over a temperature range from –57 to 232∞C (–70 to 450∞F).

8.6.4.2 Metallic Hoses The construction of a braided, flexible all-metal hose includes a tube of corrugated bronze. The tube is covered with the woven metallic braid to protect against abrasion, and to provide increased resistance to pressure. Metal hose is also available in steel, aluminum, Monel®, stainless steel, and other corrosion-resistant metals in diameters up to 3 in. and in lengths of 24 in.

In addition to providing protection against abrasion and resistance to pressure, the flexible metal hose also dampens vibration. For example, a plant air compressor produces a considerable amount of vibration. The flexible hoses from such machines increase mobility for portable equipment and dampen the vibration. Other considerations such as constant bending at high temperatures and pressures are extremely detrimental on most other types of hoses.

Other common uses for metallic hoses include serving as steam lines, lubricating lines, gas and oil lines, and exhaust hose for diesel engines. The corrugated type, for © 2003 by CRC Press LLC

example, is used for high-temperature, high-pressure leakproof service. Another type of construction is the interlocked flexible metal hose, used mainly for low-pressure applications. The standard shop oil can use a flexible hose for the flexible spout. Other metal hoses, with a liner of flexible, corrosion-resistant material, are available in diameters of up to 24 in.

Another type of metallic hose is used in ductwork.

These are usually made of aluminum, galvanized steel, and stainless steel. They are used to protect against corrosive fumes, as well as gases at extreme hot or cold temperatures. They usually do not burn because they are also fire resistant.

8.6.5 HOSE COUPLINGS The methods of connecting or coupling hoses vary. Hose couplings may be either permanent or reusable. They can also be manufactured for the obvious advantage of quickconnect or quick-disconnect. Probably the best example of the need for quick-connect is fire hose — quickdisconnect couplings permit rapid connection between separate lengths of hose, and between hose ends and hydrants or nozzles. Another good example of where the quick-connect, quick-disconnect feature is user-friendly is in plant or mobile compressed air systems — a single line may have a number of uses. Changes involve disconnecting one section and connecting another. In plant shops, for example, compressed air from a single source is used to power pneumatic tools, cleaning units, paint sprayers, and so on. Each unit has a hose that is equipped for rapid connecting and disconnecting at the fixed airline.

Important Point: Caution: Before connections are broken, unless quick-acting, self-closing connectors are used, pressure must be released first.

For general low-pressure applications, a coupling like that shown in Figure 8.25 is used. To place this coupling on the hose by hand, first cut hose to proper length, and then oil inside of hose and outside of the coupling stem.

Force the hose over the stem into the protective cap until it seats against bottom of the cap. No brazing is involved, and the coupling can be used repeatedly. After the coupling has been inserted in the hose, a yoke is placed over it in such a way that its arms are positioned along opposite sides of the hose behind the fitting. The arms are then tightly strapped or banded.

Important Point: Caution: Where the pressure demands are greater, such a coupling can be blown out of the tube. Hose couplings designed to meet high-pressure applications must be used.

A variation of this type uses a clamp that is put over the inner end of the fitting and is then tightly bolted, thus

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To maintain a hose, we should:

FIGURE 8.25 Low-pressure hose coupling. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

1. Examine for cracks in the cover caused by weather, heat, oil, or usage.

2. Look for a restricted bore because of tubeswelling or foreign objects.

3. Look for cover blisters, which permit material pockets to form between carcass and cover.

4. Look for leaking materials, which is usually caused by improper couplings or faulty fastenings of couplings.

5. Look for corrosion damage to couplings.

6. Look for kinked or otherwise damaged hose.

Important Point: Caution: Because any of the faults listed above can result in a dangerous hose failure, regular inspection is necessary. At the first sign of weakness or failure, replace the hose.

System pressure and temperature gauges should be checked regularly. Do not allow the system to operate above design conditions â&#x20AC;&#x201D; especially when hose is a component of the system.

FIGURE 8.26 Coupling installation for all-metal hose. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

holding the hose firmly. In other cases, a plain clamp is used. Each size clamp is designed for a hose of a specified size (diameter). The clamp slides snugly over the hose, and is then crimped tight by means of a special hand tool or air-powered tool.

Couplings for all-metal hoses, described earlier, involve two brazing operations, as shown in Figure 8.26.

The sleeve is slipped over the hose end and brazed to it, and then the nipple is brazed to the sleeve.

Important Point: For large hoses of rugged wall construction, it is not possible to insert push-on fittings by hand. Special bench tools are required.

Quick-connect, quick-disconnect hose couplings provide flexibility in many plant process lines where a number of different fluids or dry chemicals from a single source are either to be blended or routed to different vats or other containers. Quick-connect couplings can be used to pump out excavations, manholes, and so forth. They would not be used where highly corrosive materials are involved.

8.6.6 HOSE MAINTENANCE All types of equipment and machinery require proper care and maintenance, including hoses. Depending on the hose type and its application, some require more frequent checking than others. The maintenance procedures required for most hoses are typical, and are outlined here as an example. Š 2003 by CRC Press LLC

8.7 PIPE AND TUBE FITTINGS The term piping refers to the overall network of pipes or tubing, fittings, flanges, valves, and other components that comprise a conduit system used to convey fluids. Whether a piping system is used to simply convey fluids from one point to another or to process and condition the fluid, piping components serve an important role in the composition and operation of the system. A system used solely to convey fluids may consist of relatively few components, such as valves and fittings, whereas a complex chemical processing system may consist of a variety of components used to measure, control, condition, and convey the fluids.

In this section, the characteristics and functions of various piping and tubing fittings are described.36

8.7.1 FITTINGS The primary function of fittings is to connect sections of piping and tubing and to change direction of flow. Whether used in piping or tubing, fittings are similar in shape and type, even though pipefittings are usually heavier than tubing fittings. Several methods can be used to connect fittings to piping and tubing systems. However, most tubing is threadless because it does not have the wall thickness needed to carry threads. Most pipes, on the other hand, because they have heavier walls, are threaded.

In regard to changing direction of flow, the simplest way would be simply to bend the conduit; this is not always practical or possible. When piping is bent, it is usually accomplished by the manufacturer in the production process (in larger shops equipped with their own pipe-bending

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D D

Short radius

Long radius

FIGURE 8.27 Short and long radius elbows. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

machines), but not by the maintenance operator on the job.

Tube bending, on the other hand, is a common practice.

Generally, a tubing line requires fewer fittings than a pipeline; however, in actual practice many tube fittings are used.

Important Point: Recall that improperly made bends can restrict fluid flow by changing the shape of the pipe and weakening the pipe wall.

Fittings are basically made from the same materials (and in the same broad ranges of sizes) as piping and tubing, including bronze, steel, cast iron, glass, and plastic.

Various established standards are in place to ensure that fittings are made from the proper materials and are able to withstand the pressures required; they are also made to specific tolerances, so that they will properly match the piping or tubing that they join. A fitting stamped 200 lb, for example, is suitable (and safe) for use up to 200 psi.

8.7.2 FUNCTIONS

OF

FITTINGS

Fittings in piping and tubing systems have five main functions: 1.

2.

3.

4.

5.

Changing the direction of flow Providing branch connections Changing the sizes of lines Closing lines Connecting lines

8.7.2.1 Changing the Direction of Flow Usually a 45∞ or 90∞ elbow (or ell) fitting is used to change the direction of flow. Elbows are among the most commonly used fittings in piping, and are occasionally used in tubing systems.

Two types of 90∞ elbows are shown in Figure 8.27. From the figure, it is apparent that the long-radius fitting (the most preferred elbow) has the more gradual curve of the two. This type of elbow is used in applications where the rate of flow is critical, and space presents no problem. Flow loss caused by turbulence is minimized by the gradual curve. © 2003 by CRC Press LLC

D FIGURE 8.28 Long-radius return bend. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

The short-radius elbow (see Figure 8.27) should not be used in a system made up of long lines and has many changes in direction. Because of the greater frictional loss in the short-radius elbow, heavier and more expensive pumping equipment may be required.

Figure 8.28 shows a return bend fitting that carries fluid through a 180∞ (hairpin) turn. This type of fitting is used for piping in heat exchangers and heater coils. Note that tubing, which can be bent into this form, does not require any fittings in this kind of application.

8.7.2.2 Providing Branch Connections Because they are often more than single lines running from one point to another point, piping and tubing systems usually have a number of intersections. In fact, many complex piping and tubing systems resemble the layout of a town or city.

8.7.2.3 Changing the Sizes of Lines For certain applications, it is important to reduce the volume of fluid flow or to increase flow pressure in a piping or tubing system. To accomplish this, a reducer (which reduces a line to a smaller pipe size) is commonly used.

Important Point: Reducing is also sometimes accomplished by means of a bushing inserted into the fitting.

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Plug Gate valve

Union Cross

Y-fitting

Reducing coupling Tee

Reducing bushing

Cap

45° elbow 90° elbow

FIGURE 8.29 Diagram of a hypothetical shortened piping system. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

8.7.2.4 Sealing Lines Pipe caps are used to seal or close off (similar to corking a bottle) the end of a pipe or tube. Usually, caps are used in a part of the system that has been dismantled.

To seal off openings in fittings, plugs are used. Plugs also provide a means of access into the piping or tubing system, in case the line becomes clogged.

FIGURE 8.30 Flanged fitting. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

8.7.2.5 Connecting Lines To connect two lengths of piping or tubing together, a coupling or union is used. A coupling is simply a threaded sleeve. A union is three-piece device that includes a threaded end, an internally threaded bottom end, and a ring. A union does not change the direction of flow, close off the pipe, or provide for a branch line. Unions make it easy to connect or disconnect pipes without disturbing the position of the pipes.

Figure 8.29 is a diagram of a shortened piping system that illustrates how some fittings are used in a piping system. (Note: Figure 8.29 is only for illustrative purposes; it is unlikely that such a system with so many fittings would actually be used.)

threads must be properly cut to ensure the weakest link is not further compromised.

Typically, the method used to ensure a good seal in a threaded fitting is to coat the threads with a paste dope.

Another method is to wind the threads with Teflon® tape.

8.7.3 TYPES

8.7.3.2 Flanged Connections

OF

CONNECTIONS

Pipe connections may be screwed, flanged, or welded.

Each method is widely used, and each has its own advantages and disadvantages.

8.7.3.1 Screwed Fittings Screwed fittings are joined to the pipe by means of threads.

The main advantage of using threaded pipefittings is that they can be easily replaced. The actual threading of a section of replacement pipe can be accomplished on the job. The threading process itself, which cuts right into the pipe material, may weaken the pipe in the joint area.

The weakest link in a piping system is the connection point. Because threaded joints can be potential problem areas, especially where higher pressures are involved, the © 2003 by CRC Press LLC

FIGURE 8.31 Flanged joint. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Figure 8.30 shows a flanged fitting. Flanged fittings are forged or cast iron pipe. The flange is a rim at the end of the fitting, which mates with another section. Pipe sections are also made with flanged ends.

Flanges are joined either by being bolted or welded together. The flange faces may be ground and lapped to provide smooth, flat mating surfaces. Obviously, a tight joint must be provided to prevent leakage of fluid and pressure.

Figure 8.31 shows a typical example of a flanged joint.

The mating parts are bolted together with a gasket inserted between their faces to ensure a tight seal. The procedure requires proper alignment of clean parts and tightening of bolts.

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Important Point: Some flanges have raised faces and others have plain faces. Like faces must be matched; a flange with a raised face should never be joined to one with a plain face.

8.7.3.3 Connections Currently, because of improvements in piping technology and welding techniques and equipment, the practice of using welded joints is increasing. When properly welded, a piping system forms a continuous system, combining piping, valves, flanges, and other fittings. Along with providing a long leak-proof and maintenance-free life, the smooth joints simplify insulation and take up less room.

8.7.4 TUBING FITTINGS

AND

CONNECTIONS

Tubing is connected by brazed or welded flange fittings, compression fittings, and flare fittings.

The welded flange connection is a reliable means of connecting tubing components. The flange welded to the tube end fits against the end of the fitting. The locknut of the flange is then tightened securely onto the fitting.

The compression fitting connection uses a ferrule that pinches the tube as the locknut is tightened on the body of the fitting.

The flare fitting connection uses tubing flared on one end of the tubing that matches the angle of the fitting. The tubeâ&#x20AC;&#x2122;s flared end is butted against the fitting, and a locknut is screwed tightly onto the fitting, sealing the tube connection properly.

Other fittings used for flanged connections include expansion joints and vibration dampeners.

Expansion joints function to compensate for slight changes in the length of pipe by allowing joined sections of rigid pipe to expand and contract with changes in temperature. They also allow pipe motion, either along the length of the pipe or to the side, as the pipe shifts around slightly after installation. Finally, expansion joints also help dampen vibration and noise carried along the pipe from distant equipment (e.g., pumps).

One type of expansion joint has a leak-proof tube that extends through the bore and forms the outside surfaces of the flanges. Natural or synthetic rubber compounds are normally used, depending on the application.

Other types of expansion joints include metal corrugated types, slip-joint types, and spiral-wound types. In addition, high-temperature lines are usually made up with a large bend or loop to allow for expansion.

Vibration dampeners absorb vibrations that, unless reduced, could shorten the life of the pipe and the service life of the operating equipment. They also eliminate line humming and hammering (water hammer) carried by the pipes. Š 2003 by CRC Press LLC

8.8 VALVES Any water or wastewater operation will have many valves that require attention. Simply as a matter of routine, a maintenance operator must be able to identify and locate different valves in order to inspect them, adjust them, and repair or replace them. For this reason, the operator should be familiar with all valves, especially those that are vital parts of a piping system.

A valve is defined as any device by which the flow of fluid may be started, stopped, or regulated by a movable part that opens or obstructs passage. As applied in fluid power systems, valves are used for controlling the flow, the pressure, and the direction of the fluid flow through a piping system. The fluid may be a liquid, a gas, or some loose material in bulk (like a biosolids slurry). Designs of valves vary, but all valves have two features in common: a passageway through which fluid can flow and some kind of movable (usually machined) part that opens and closes the passageway.37 Important Point: It is all but impossible to operate a practical fluid power system without some means of controlling the volume and pressure of the fluid and directing the flow of fluid to the operating units. This is accomplished by the incorporation of different types of valves.

Whatever type of valve is used in a system, it must be accurate in the control of fluid flow and pressure and the sequence of operation. Leakage between the valve element and the valve seat is reduced to a negligible quantity by precision-machined surfaces, resulting in carefully controlled clearances. This is one of the very important reasons for minimizing contamination in fluid power systems. Contamination causes valves to stick; plugs small orifices; and causes abrasions of the valve seating surfaces, which result in leakage between the valve element and valve seat when the valve is in the closed position. Any of these can result in inefficient operation or complete stoppage of the equipment. Valves may be controlled manually, electrically, pneumatically, mechanically, hydraulically, or by combinations of two or more of these methods. Factors that determine the method of control include the purpose of the valve, the design and purpose of the system, the location of the valve within the system, and the availability of the source of power.

Valves are made from bronze, cast iron, steel, MonelÂŽ, stainless steel, and other metals. They are also made from plastic and glass (see Table 8.1). Special valve trim is used where seating and sealing materials are different from the basic material of construction (see Table 8.2). (Note: Valve trim usually means those internal parts of a valve controlling the flow and in physical contact with the line fluid.)

Valves are made in a full range of sizes, which match pipe and tubing sizes. Actual valve size is based upon the

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TABLE 8.1 Valves: Materials of Construction Cast iron Ductile iron Carbon steel Stainless steel Copper alloy High Duty alloys Other metals Nonmetals

Grey cast iron; also referred to as flake graphite iron May be malleable iron or spheroidal graphite (nodular) cast iron May be as steel forgings or steel castings, according to the method of manufacture; carbon steel valves may also be manufactured by fabrication using wrought steels May also be in the form of forgings, castings, or wrought steels for fabrication May be gunmetal, bronze, or brass; aluminum bronze may also be used.

Are usually those nickel or nickel molybdenum alloys manufactured under various trade names Are those pure metals having extreme corrosion resistance such as titanium or aluminum Are typically the plastics materials such as PVC or polypropylene

Source: From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.

TABLE 8.2 Valve Trim Metal seating Soft seating Lined

Is commonly used in gate and globe valves, and in the latter particularly for control applications where seatings may additionally be coated with hard metal Is commonly used in ball, butterfly, and diaphragm valves; seatings may be made from a wide variety of elastomers and polymers, including fluorocarbons.

Valves are usually made in cast iron with an internal lining of elastomer of polymer material; inorganic materials such as glass, together with metals such as titanium are so used for lining; lining thickness will depend upon design and the type of material used; in many cases, the valve lining will also form the seating trim

Source: From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.

TABLE 8.3 Valve End Connections Flanged

Threaded Other

Valves will normally be supplied with flanges confirming to either BS4505 (equivalent to DIN) or BS 1560 (equivalent to ANSI) according to specification; manufacturers may be able to supply valves with flanges to other standards Valves will normally be supplied with threads to BS21 (ISO/7) parallel or taper End connections include butt or socket weld ends and wafer valves designed to fit between pipe flanges.

Source: From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.

internationally agreed definition of nominal size. Nominal size (DN) is a numerical designation of size that is common to all components in a piping system other than components designated by outside diameters. It is a convenient number for reference purposes and is only loosely related to manufacturing dimensions. Valves are made for service at the same pressures and temperatures that piping and tubing is subject to.

Valve pressures are based upon the internationally agreed definition of nominal pressure. Nominal pressure (PN) is a pressure that is conventionally accepted or used for reference purposes. All equipment of the same DN designated by the same PN number must have the same mating dimensions appropriate to the type of end connecŠ 2003 by CRC Press LLC

tions. The permissible working pressure depends upon materials, design, and working temperature; it should be selected from the (relevant), pressure/temperature tables.

The pressure rating of many valves is designated under the ANSI class system. The equivalent class rating to PN ratings is based upon international agreement.

Usually, valve end connections are classified as flanged, threaded, or other (see Table 8.3).

Valves are also covered by various codes and standards, as are the other components of piping and tubing systems.

Many valve manufacturers offer valves with special features. Table 8.4 lists a few of these special features.

This is not an exhaustive list and for more details of other features, the manufacturer should be consulted.

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TABLE 8.4 Valve Special Features High temperature Cryogenic Bellows sealed Actuated Fire tested design

Valves are those usually able to operate continuously on services above 250∞C Valves are those that will operate continuously on services in the range –50 to 196∞C Valves are glandless designs having a metal bellows for stem sealing Valves may be operated by a gearbox, pneumatic, or hydraulic cylinder (including diaphragm actuator), or electric motor and gearbox Refers to a valve that has passed a fire test procedure specified in an appropriate inspection standard

Source: From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.

Handwheel

Stem Closing element

Stuffing box Body Outlet

Inlet

Open

Closed

FIGURE 8.32 Basic valve operation. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

The different types of valves used in fluid power systems, their classifications, and their applications are discussed in this chapter.

8.8.1 VALVE CONSTRUCTION Figure 8.32 shows the basic construction and principle of operation of a common valve type. Fluid flows into the valve through the inlet. The fluid flows through passages in the body and past the opened element that closes the valve. It then flows out of the valve through the outlet or discharge.

If the closing element is in the closed position, the passageway is blocked. Fluid flow is stopped at that point.

The closing element keeps the flow blocked until the valve is opened again. Some valves are opened automatically, and manually operated hand wheels control others. Other valves, such as check valves, operate in response to pressure or the direction of flow.

A seal is used to prevent leakage whenever the closing element is positioned in the closed position. In Figure 8.34, the seal consists of a stuffing box fitted with packing. The closing element fits against the seat in the valve body to keep the valve tightly closed. © 2003 by CRC Press LLC

8.8.2 TYPES

OF

VALVES

The types of valves covered in this text include the following: 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Ball valves Gate valves Globe valves Needle valves Butterfly valves Plug valves Check valves Quick-opening valves Diaphragm valves Regulating valves Relief valves Reducing valves

Each of these valves is designed to perform either control of the flow, the pressure, and the direction of fluid flow or for some other special application. With a few exceptions, these valves take their names from the type of internal element that controls the passageway. The exceptions are the check valve, quick-opening valve, regulating valve, relief valve, and reducing valves.

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8.8.2.1 Ball Valves Ball valves, as the name implies, are stop valves that use a ball to stop or start fluid flow. The ball performs the same function as the disk in other valves. As the valve handle is turned to open the valve, the ball rotates to a point where part or all of the hole through the ball is in line with the valve body inlet and outlet, allowing fluid to flow through the valve. When the ball is rotated so the hole is perpendicular to the flow openings of the valve body, the flow of fluid stops.

Most ball valves are the quick-acting type. They require only a 90-degree turn to either completely open or close the valve. However, many are operated by planetary gears. This type of gearing allows the use of a relatively small hand wheel and operating force to operate a large valve. The gearing increases the operating time for the valve. Some ball valves also contain a swing check located within the ball to give the valve a check valve feature.

The two main advantages of using ball valves are: (1) the fluid can flow through it in either direction, as desired; and (2) when closed, pressure in the line helps to keep it closed.

8.8.2.2 Gate Valves Gate valves are used when a straight-line flow of fluid and minimum flow restriction are needed; they are the most common type of valve found in a water distribution system.

Gate valves are so named because the part that either stops or allows flow through the valve acts somewhat like a gate.

The gate is usually wedge-shaped. When the valve is wide open, the gate is fully drawn up into the valve bonnet. This leaves an opening for flow through the valve the same size as the pipe in which the valve is installed. For these reasons, the pressure loss (pressure drop) through these types of valves is about equal to the loss in a piece of pipe of the same length. Gate valves are not suitable for throttling (means to control the flow as desired, by means of intermediate steps between fully open and fully closed) purposes.

The control of flow is difficult because of the valve’s design, and the flow of fluid slapping against a partially open gate can cause extensive damage to the valve.

FIGURE 8.33 Globe valve. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

and other household plumbing. As illustrated in Figure 8.33, the valves have a circular disk — the globe — that presses against the valve seat to close the valve. The disk is the part of the globe valve that controls flow. The disk is attached to the valve stem. As shown in Figure 8.33, fluid flow through a globe valve is at right angles to the direction of flow in the conduits. Globe valves seat very tightly, and can be adjusted with fewer turns of the wheel than gate valves; they are preferred for applications that call for frequent opening and closing. On the other hand, globe valves create high head loss when fully open; they are not suited in systems where head loss is critical.

Important Point: The globe valve should never be jammed in the open position. After a valve is fully opened, the hand wheel should be turned toward the closed position approximately onehalf turn. Unless this is done, the valve is likely to seize in the open position, making it difficult, if not impossible, to close the valve. Another reason for not leaving globe valves in the fully open position is that it is sometimes difficult to determine if the valve is open or closed.39 8.8.2.4 Needle Valves Although similar in design and operation to the globe valve (a variation of globe valves), the needle valve has a closing element in the shape of a long tapered point that is at the end of the valve stem. Figure 8.34 shows a crosssectional view of a needle valve; the long taper of the valve closing element permits a much smaller seating

Important Point: Gate vales are well suited to service on equipment in distant locations where they may remain in the open or closed position for a long time. Generally, gate valves are not installed where they will need to be operated frequently because they require too much time to operate from fully open to closed.38 8.8.2.3 Globe Valves Probably the most common valve type in existence, the globe valve principle is commonly used for water faucets © 2003 by CRC Press LLC

FIGURE 8.34 Common needle valve. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

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Flow Flow FIGURE 8.35 Cross-section of butterfly valve. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

surface area than the globe valveâ&#x20AC;&#x2122;s; accordingly, the needle valve is more suitable as a throttle valve. In fact, needle valves are used for very accurate throttling.

When the direction of flow reverses, the valve closes automatically from the fluid pressure against it.

There are several types of check valves used in water and wastewater operations, including

8.8.2.5 Butterfly Valves Figure 8.35 shows a cross-sectional view of a butterfly valve.

The valve consists of a body in which a disk (butterfly) rotates on a shaft to open or close the valve. Butterfly valves may be flanged or wafer design, the latter intended for fitting directly between pipeline flanges. In the full open position, the disk is parallel to the axis of the pipe and the flow of fluid. In the closed position, the disk seals against a rubber gasket-type material bonded either on the valve seat of the body or on the edge of the disk. Because the disk of a butterfly valve stays in the fluid path in the open position, the valve creates more turbulence (higher resistance to flow, equaling a higher pressure loss) than a gate valve.

On the other hand, butterfly valves are compact. They can also be used to control flow in either direction. This feature is useful in water treatment plants that periodically backwash to clean filter systems.

8.8.2.6 Plug Valves A plug valve (also known as a cock, or petcock) is similar to a ball valve. Plug valve properties include: 1. High capacity operation, quarter-turn operation 2. A cylindrical or conical plug used as the closing member 3. Directional 4. Moderate vacuum service 5. Flow throttling with interim positioning 6. Simple construction; o-ring seal 7. Not necessarily full on and off 8. Easily adapted to automatic control 9. Safely handles gases and liquids 8.8.2.7 Check Valves Check valves are usually self-acting and designed to allow the flow of fluid in one direction only. They are commonly used at the discharge of a pump to prevent backflow when the power is turned off. When the direction of flow is moving in the proper direction, the valve remains open. Š 2003 by CRC Press LLC

1.

2.

3.

4.

5.

6.

7.

Slanting disk check valves Cushioned swing check valves Rubber flapper swing check valves Double door check valves Ball check valves Foot valves Backflow prevention devices

In each case, pressure from the flow in the proper direction pushes the valve element to an open position.

Flow in the reverse direction pushes the valve element to a closed position.

Important Point: Check valves are also commonly referred to as nonreturn or reflux valves.

8.8.2.8 Quick-Opening Valves Quick-opening valves are nothing more than adaptations of some of the valves already described. Modified to provide a quick on and off action, they use a lever device in place of the usual threaded stem and control handle to operate the valve. This type of valve is commonly used in water and wastewater operations where deluge showers and emergency eyewash stations are installed in work areas where chemicals are loaded and transferred, and chemical systems are maintained. They also control the air supply for some emergency alarm horns, around chlorine storage areas, for example. Moreover, they are usually used to cut off the flow of gas to a main or to individual outlets.

8.8.2.9 Diaphragm Valves Diaphragm valves are glandless valves that use a flexible elastomeric diaphragm (a flexible disk) as the closing member and also affect an external seal. They are well suited to service in applications where tight, accurate closure is important. The tight seal is effective whether the fluid is a gas or a liquid. This tight closure feature makes these valves useful in vacuum applications. Diaphragm valves operate similar to globe valves and are usually multiturn in operation; they are available as weir type and full bore. A common application of diaphragm valves in

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Plug-type disk angle valve

Pressure gauge Safety valve

Pressure-regulating valve

Gate valve

Gate valve

FIGURE 8.36 Pressure-regulating valve system. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

water and wastewater operations is to control fluid to an elevated tank.

8.8.2.10 Regulating Valves As their name implies, regulating valves regulate either pressure or temperature in a fluid line, keeping them very close to a preset level. If the demands and conditions of a fluid line remained steady at all times, no regulator valve would be needed. In the real world, ideal conditions do not occur.

Pressure-regulating valves regulate fluid pressure levels to meet flow demand variations. Flow variations vary with the number of pieces of equipment in operation, and the change in demand as pumps and other machines operate. In such fluid line systems, demands are constantly changing. Probably the best example of this situation is seen in the operation of the plantâ&#x20AC;&#x2122;s low-pressure air supply system. For shop use, no more than 30 psi air is usually required (depending on required usage, of course). This air is supplied by the plantâ&#x20AC;&#x2122;s air compressor, which normally operates long enough to fill an accumulator with pressurized air at a set pressure level. When shop air is required, for whatever reason, compressed air is drawn from the connection point in the shop. The shop connection point is usually connected via a pressure reducer (sets the pressure at the desired usage level) that is fed from the accumulator where the compressed air is stored. If the user draws a large enough quantity of compressed air from the system (from the accumulator), a sensing device within the accumulator will send a signal to the air compressor to start, producing compressed air to recharge the accumulator.

As well as providing service in airlines, pressureregulating valves are also used in liquid lines. The operating principle is much the same for both types of service.

Simply, the valve is set to monitor the line, and to make Š 2003 by CRC Press LLC

needed adjustments in response to a signal from a sensing device.

Temperature-regulating valves (also referred to as thermostatic control valves) are closely related to pressureregulating valves (see Figure 8.36). Their purpose is to monitor the temperature in a line or process solution tank, and to regulate it, raising or lowering the temperature as required.

In water and wastewater operations, probably the most familiar application where temperature-regulating valves (see Figure 8.37) are used is in heat exchangers. A heat exchanger-type water system utilizes a water-to-coolant heat exchanger for heat dissipation. This is an efficient and effective method to dispose of unwanted heat. Heat exchangers are equipped with temperature regulating valves that automatically modulate the shop process water, limiting usage to just what is required to achieve the desired coolant temperature.

Tubing

Control unit

Bulb

Valve body Closing element FIGURE 8.37 Temperature-regulating valve assembly. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

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8.8.2.11 Relief Valves Some fluid power systems, even when operating normally, may temporarily develop excessive pressure. For example, whenever an unusually strong work resistance is encountered, dangerously high pressure may develop. Relief valves are used to control this excess pressure. Such valves are automatic valves; they start to open at a preset pressure, but require a 20% overpressure to open wide. As the pressure increases, the valve continues to open further until it has reached its maximum travel. As the pressure drops, it starts to close, and finally shuts off at about the set pressure.

Main system relief valves are generally installed between the pump or pressure source and the first system isolation valve. The valve must be large enough to allow the full output of the hydraulic pump to be delivered back to the reservoir.

Important Point: Relief valves do not maintain flow or pressure at a given amount, but prevent pressure from rising above a specific level when the system is temporarily overloaded.

8.8.2.12 Reducing Valves Pressure-reducing valves provide a steady pressure into a system that operates at a lower pressure than the supply system. In practice, they are very much like pressureregulating valves. A pressure-reducing valve reduces pressure by throttling the fluid flow. A reducing valve can normally be set for any desired downstream pressure within the design limits of the valve. Once the valve is set, the reduced pressure will be maintained regardless of changes in supply pressure (as long as the supply pressure is at least as high as the reduced pressure desired) and regardless of the system load, providing the load does not exceed the design capacity of the reducer.

8.8.3 VALVE OPERATORS In many modern water and wastewater operations, devices called operators or actuators mechanically operate many valves. These devices â&#x20AC;&#x201D; pneumatic, hydraulic, and magnetic operators â&#x20AC;&#x201D; may be operated by air, electricity, or fluid.

8.8.3.1 Pneumatic and Hydraulic Valve Operators Pneumatic and hydraulic valve operators are much the same in appearance and work in much the same way.

Hydraulic cylinders using either plant water pressure or hydraulic fluid frequently operate valves in treatment plants and pumping stations.40 In a typical pneumatic ballvalve actuator, the cylinder assembly is attached to the Š 2003 by CRC Press LLC

ball-valve stem close to the pipe. A piston inside the cylinder can move in either direction. The piston rod is linked to the valve stem, opening or closing the valve, depending on the direction in which the piston is traveling. As a failsafe feature, some of these valves are spring-loaded. In case of hydraulic or air pressure failure, the valve operator returns the valve to the safe position.

Note: According to Casada, valve operators and positioners usually require more maintenance than the valves themselves.41 8.8.3.2 Magnetic Valve Operators Magnetic valve operators use electric solenoids. A solenoid is a coil of magnetic wire, roughly in the shape of a doughnut. When a bar of iron is inserted as a plunger mechanism inside an energized coil, it moves along the coil because of the magnetic field that is created. If the plunger (the iron bar) is fitted with a spring, it returns to its starting point when the electric current is turned off.

Solenoids are used as operators for many different types of valves used in water and wastewater operations.

For example, in a direct-operating valve, the solenoid plunger is used in place of a valve stem and hand wheel.

The plunger is connected directly to the disk of a globe valve. As the solenoid coil is energized or deenergized, the plunger rises or falls, operating or closing the valve.

8.8.4 VALVE MAINTENANCE As with any other mechanical device, effective valve maintenance begins with its correct operation. As an example of incorrect operation, consider the standard household water faucet. As the faucet washers age, they harden and deteriorate. The valve becomes more difficult to operate properly, and eventually, the valve begins to leak. A common practice is simply to apply as much force as possible to the faucet handle. Unfortunately, this damages the valve stem and the body of the valve body.

Good maintenance includes preventive maintenance, which, in turn, includes inspection of valves, correct lubrication of all moving parts, and the replacement of seals or stem packing.

8.9 PIPING SYSTEM: PROTECTIVE DEVICES Piping systems must be protected from the harmful effects of undesirable impurities (solid particles) entering the fluid stream. Because of the considerable variety of materials carried by piping systems, there is an equal range of choices in protective devices. Such protective devices include strainers, filters, and traps.

In this section, we describe the design and function of strainers, filters, and traps. The major maintenance considerations of these protective devices also are explained.

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8.9.1 APPLICATIONS Filters, strainers, and traps are normally thought of in terms of specific components used in specific systems.

However, it is important to keep in mind that the basic principles apply in many systems. While the examples used in this chapter include applications found in water/wastewater treatment, collection, and distribution systems, the applications are also found in almost every plant â&#x20AC;&#x201D; hot and cold water lines, lubricating lines, pneumatic and hydraulic lines, and steam lines.

In regards to steam lines, it is important to point out that in our discussion of traps, their primary application is in steam systems where they remove unwanted air and condensate from lines.

Important Point: A very large percentage (estimated to be >70%) of all plant facilities in the U.S. make use of steam in some applications.

Other system applications of piping protective devices include conveyance of hot and chilled water for heating and air conditioning, and lines that convey fluids for various processes. Any foreign contamination in any of these lines can cause potential trouble. Piping systems can become clogged, thereby causing greatly increased friction and lower line pressure. Foreign contaminants (dirt and other particles) can also damage valves, seals, and pumping components.

Important Point: Foreign particles in a high-pressure line can damage a valve by clogging the valve so that it cannot close tightly. In addition, foreign particles may wear away the closely machined valve parts.

8.9.2 STRAINERS42 Strainers, usually wire mesh screens, are used in piping systems to protect equipment sensitive to contamination that may be carried by the fluid. Strainers can be used in pipelines conveying air, gas, oil, steam, water, wastewater, and nearly any other fluid conveyed by pipes. Generally, strainers are installed ahead of valves, pumps, regulators, and traps in order to protect them against the damaging effects of corrosion products that may become dislodged and conveyed throughout the piping system.

A common strainer is shown in Figure 8.38. This type of strainer is generally used upstream of traps, control valves, and instruments. This strainer resembles a lateral branch fitting with the strainer element installed in the branch. The end of the lateral branch is removable to permit servicing of the strainer.

In operation, the fluid passes through the strainer screen, which catches most of the contaminants. Then the fluid passes back into the line. Contaminants in the fluid are caught in two ways. Either they do not make it through Š 2003 by CRC Press LLC

FIGURE 8.38 A common strainer. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

the strainer screen, or they do not make the sharp turn that the fluid must take as it leaves the unit. The bottom of the unit serves as a sump where the solids collect. A blowout connection may be provided in the end cap to flush the strainer. The blowout plug can be removed, and the pressure in the line can be used to blow the fixture clean.

Important Point: Before removing the blowout plug, the valve system must be locked out or tagged out first.

8.9.3 FILTERS The purpose of any filter is to reduce or remove impurities or contaminants from a fluid (liquid or gas) to an acceptable or predetermined level. This is accomplished by passing the fluid through some kind of porous barrier. Filter cartridges have replaceable elements made of paper, wire cloth, nylon cloth, or fine-mesh nylon cloth between layers of coarse wire. These materials filter out unwanted contaminants that collect on the entry side of the filter element.

When clogged, the element is replaced.

Most filters operate in two ways: (1) they cause the fluid to make sharp changes in direction as it passes through (this is important because the larger particles are too heavy to change direction quickly); and (2) they contain some kind of barrier that will not let larger contaminants pass.

8.9.4 TRAPS43 Traps, used in steam processes, are automatic valves that release condensate (condensed steam) from a steam space while preventing the loss of live steam. Condensate is undesirable because water produces rust and water plus steam leads to water hammer. In addition, steam traps remove air and noncondensate from the steam space.

The operation of a trap depends on what is called differential pressure (or delta-P), in pounds per square inch. Differential pressure is the difference between the inlet and outlet pressures. A trap will not operate correctly

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FIGURE 8.40 A float-and-thermostatic trap. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

FIGURE 8.39 A thermostatic trap (shown in the open position).

(From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

at a differential pressure higher than the one of which it was designed.

There are many types of steam traps because there are many different types of applications. Each type of trap has a range of applications for which it is best suited. For example, thermostatic and float-and-thermostatic are the names given to the two general types of traps.

Thermostatic traps have a corrugated bellows-operating element that is filled with an alcohol mixture that has a boiling point lower than that of water (see Figure 8.39).

The bellows contracts when in contact with condensate and expands when stream is present. If a heavy condensate load occurs, the bellows will remain in the contracted state, allowing condensate to flow continuously. As steam builds up, the bellows closes. At times the trap acts as a continuous flow type, while at other times it acts intermittently as it opens and closes to condensate and stream, or it may remain totally closed.

Important Point: The thermostatic trap is designed to operate at a definite temperature drop a certain number of degrees drop below the saturated temperature for the existing steam pressure.

A float-and-thermostatic trap is shown in Figure 8.40.

It consists of a ball float and a thermostatic bellows element.

As condensate flows through the body, the float rises and falls, opening the valve according to the flow rate. The thermostatic element discharges air from the steam lines.

They are suitable in heavy and light loads and on high and low pressure, but are not recommended where water hammer is a possibility. Š 2003 by CRC Press LLC

8.9.4.1 Trap Maintenance and Testing Because they operate under constantly varying pressure and temperature conditions, traps used in steam systems require maintenance. Just as significant, traps can fail due to these varying conditions. When they do fail, most traps fail in the open mode, which may require the boiler to work harder to perform a task that, in turn, can create high backpressure to the condensate system. This inhibits discharge capacities of some traps, which may be beyond their rating and cause system inefficiency.

Important Point: While it is true that most traps operate with backpressure, it is also true that they do so only at a percentage of their rating, affecting everything down the line of the failed trap.

Steam quality and product can be affected.

A closed trap produces condensate back up into the steam space. The equipment cannot produce the intended heat. Consider, as an example, a four-coil dryer with only three coils operating. In this setup, it will take longer for the dryer to dry a product, which has a negative effect on production.

8.9.4.1.1 Trap Maintenance Excluding design problems, two of the most common causes of trap failure are oversizing and dirt. Oversizing causes traps to work too hard. In some cases, this can result in blowing of live steam. For example, certain trap types can lose their prime due to an abrupt change in pressure. This will cause the valve to open.

Traps tend to accumulate dirt (sludge) that prevents tight closing. The moving parts of the traps are subject to wear. Because the moving parts of traps operate in a mixture of steam and water, or sometimes in a mixture of compressed air and water, they are difficult to lubricate.

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Important Point: Dirt (sludge) is generally produced from pipe scale or from overtreating of chemicals in a boiler.

Trap maintenance includes periodic cleaning, removing dirt that interferes with valve action, adjusting the mechanical linkage between moving parts and valves, and reseating the valves when necessary. If these steps are not taken, the trap will not operate properly.

8.9.4.1.2 Trap Testing Important Point: A word of caution is advised before testing any steam trap: Inspectors should be familiar with the particular function, review types of traps and know the various pressures within the system. This can help to ensure inspector safety, help avoid misdiagnosis, and allow proper interpretation of trap conditions.

There are three main categories of online trap inspection: visual, thermal, and acoustic. Visual inspection depends on a release valve situated downstream of certain traps. A maintenance operator opens these valves and looks to see if the trap is discharging condensate or steam. Thermal inspection relies on upstream or downstream temperature variations in a trap. It includes pyrometry, infrared, heat bands (wrapped around a trap, they change color as temperature increases), and heat sticks (which melt at various temperatures). Acoustic techniques require a maintenance operator to listen to and detect steam trap operations and malfunction. This method includes various forms of listening devices such as medical stethoscopes, screwdrivers, mechanical stethoscopes, and ultrasonic detection instruments.

Important Point: A simple trap test, which involves just listening to the trap action, tells us how the trap is opening and closing. Moreover, if the trap has a bypass line around it, leaky valves will be apparent when the main line to the trap is cut off, forcing all the fluid through the bypass.

8.10 PIPING ANCILLARIES Earlier we described various devices associated with process piping systems designed to protect the system. In this section, we discuss some of the most widely used ancillaries (or accessories) designed to improve the operation and control the system. These include pressure and temperature gauges, vacuum breakers, accumulators, receivers, and heat exchangers. It is important for us to know how these ancillary devices work, how to care for them, and, more importantly, how to use them. © 2003 by CRC Press LLC

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8.10.1 GAUGES To properly operate a system, any system, the operator must know certain things. For example, to operate a plant air compressor, the operator needs to know: (1) how to operate it; (2) how to maintain it; (3) how to monitor its operation; and, in many cases, (4) how to repair it. In short, the operator must know system parameters and how to monitor them.

Simply, operating parameters refer to those physical indications of system operation. The term parameter refers to a system’s limits or restrictions. For example, consider, again, the plant’s air compressor. It is important to know how the air compressor operates, or at least how to start and place the compressor on line properly. It is also equally important to determine if the compressor is operating per design.

Experienced operators know that in order to ensure that the air compressor is operating correctly (i.e., as per design), they need to monitor its operation. Again, they do this by monitoring the air compressor’s operation by observing certain parameters. Before starting any machine or system we must first perform a pre-start check to ensure that it has the proper level of lubricating oil, etc. Then after starting the compressor, we need to determine (observe) if the compressor is actually operating (normally, this is not difficult to discern considering that most air compressor systems make a lot of noise while in operation). Once in operation, our next move is to double-check system line-up to ensure that various valves in the system are correctly positioned (opened or closed). We might even go to a remote plant compressed air service outlet to make sure that the system is producing compressed air. (Note: Keep in mind that some compressed air systems have a supply of compressed air stored in an air receiver; when an air outlet is opened, air pressure might be present even if the compressor is not functioning as per design.) On the other hand, instead of using a remote outlet to test for compressed air supply, all we need do is look at the compressor air pressure gauge. This gauge should indicate that the compressor is producing compressed air.

Gauges are the main devices that provide us with parameter indications that we need to determine equipment or system operation.

Concerning the air compressor, the parameter we are most concerned about now is air pressure (gauge pressure).

Not only is correct pressure generation by the compressor important, but correct pressure in system pipes, tubes, and hoses is also essential. Keeping air pressure at the proper level is necessary mainly for four reasons: 1. Safe operation 2. Efficient, economic conveyance of air through the entire system, without waste of energy

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3. Delivery of compressed air to all outlet points in the system (the places where the air is to be used) at the required pressure 4. Prevention of too much or too little pressure (either condition can damage the system and become hazardous to personnel) We pointed out that before starting the air compressor, certain prestart checks must be made. This is important for all machinery, equipment, and systems. In the case of our air compressor example, we want to ensure that proper lubricating oil pressure is maintained. This is important because pressure failure in the lubricating line that serves the compressor can mean inadequate lubrication of bearings, and, in turn, expensive mechanical repairs.

8.10.1.1 Pressure Gauges As mentioned, many pressure-measuring instruments are called gauges. Generally, pressure gauges are located at key points in piping systems. Usually expressed in pounds per square inch, there is a difference between gauge pressure (psig) and absolute pressure (psia). Simply, gauge pressure refers to the pressure level indicated by the gauge.

However, even when the gauge reads zero, it is subject to ambient atmospheric pressure (i.e., 14.7 psi at sea level).

When a gauge reads 50 psi that is 50 lb gauge pressure (psig). The true pressure is the 50 pounds shown plus the 14.7 lb of atmospheric pressure acting on the gauge. The total of “actual” pressure is called the absolute pressure: gauge pressure plus atmospheric pressure (50 psi + 14.7 psi = 64.7). It is written 64.7 psia.

Important Point: Pressure in any fluid pushes equally in all directions. The total force on any surface is the pounds per square inch multiplied by the area in square inches. For example, a fluid under a pressure of 10 psi, pushing against an area of 5 in,2 produces a total force against that surface of 50 lb (10 ¥ 5).

8.10.1.1.1 Spring-Operated Pressure Gauges Pressure, by definition, must operate against a surface.

The most common method of measuring pressure in a piping system is to have the fluid press against some type of surface — a flexible surface that moves slightly. This movable surface is linked mechanically to a gear-lever mechanism that moves the indicator arrow to indicate the pressure on the dial (i.e., a pressure gauge).

The surface that the pressure acts against may be a disk or diaphragm, the inner surface of a coiled tube, a set of bellows, or the end of a plunger. No matter the element type, if the mechanism is fitted with a spring that resists the pressure and returns the element (i.e., the indi-

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cator pointer) back to the zero position when the spring drops to zero, it is called a spring-loaded gauge.

8.10.1.1.2 Bourdon-Tube Gauges Many pressure gauges in use today use a coiled tube as a measuring element called a Bourdon tube. (The gauge is named for its inventor, Eugene Bourdon, a French engineer.) The Bourdon tube is a device that senses pressure and converts the pressure to displacement. Under pressure, the fluid fills the tube (see Figure 8.41). Since the Bourdontube displacement is a function of the pressure applied, it may be mechanically amplified and indicated by a pointer.

Thus, the pointer position indirectly indicates pressure.

Important Point: The Bourdon-tube gauge is available in various tube shapes: helical, C-shaped or curved, and spiral. The size, shape, and material of the tube depend on the pressure range and the type of gauge desired.

8.10.1.1.3 Bellows Gauge Figure 8.42 shows how a simplified bellows gauge works.

The bellows is a convoluted unit that expands and contracts axially with changes in pressure. The pressure to be measured can be applied to either the outside or the inside of the bellows; in practice, most bellows measuring devices have the pressure applied to the outside of the bellows. When pressure is released, the spring returns the bellows and the pointer to the zero position.

8.10.1.1.4 Plunger Gauge Most of us are familiar with the simple tire-pressure gauge. This device is a type of plunger gauge. Figure 8.43 shows a plunger gauge used in industrial hydraulic systems. The bellows gauge is a spring-loaded gauge, where pressure from the line acts on the bottom of a cylindrical plunger in the center of the gauge and moves it upward.

At full pressure, the plunger extends above the gauge, indicating the measured pressure. As the pressure drops, the spring contracts to pull the plunger downward, back into the body (the zero reading indication).

Note: Spring-loaded gauges are not extremely accurate, but they are entirely adequate where there is no need for more precise readings.

8.10.1.1.5 Temperature Gauges As mentioned, ensuring that system pressures are properly maintained in equipment and piping systems is critical to safe and proper operation. Likewise, ensuring that the temperature of fluids in industrial equipment and piping systems is correct is just as critical. For measuring the temperature of fluids in industrial systems, various temperature-measuring devices are available.

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Pointer

Bourdon tube Pinion

Hairspring Scale

Link

Case

Pressure

Spiral Bourdon tube (annealed)

Stainless sector gear Vacuum stop

Pointer shaft

All stainless steel movement “S” link Pulsation dampner plate Span adjustment Case seat

Movement mounting screws Case attachment screw hole

“Rolled,” not cut threads

FIGURE 8.41 (Top) Bourdon tube gauge; (bottom) internal components. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

1000

1200 800

600 400

Spring

200

Bellows

Pressure connection

Pressure FIGURE 8.42 Bellows gauge. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

© 2003 by CRC Press LLC

FIGURE 8.43 Plunger gauge. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

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Temperature has been defined in a variety of ways.

One example defines temperature as the measure of heat (thermal energy) associated with the movement (kinetic energy) of the molecules of a substance. This definition is based on the theory that molecules of all matter are in continuous motion that is sensed as heat.

For our purposes, we define temperature as the degree of hotness or coldness of a substance measured on a definite scale. Temperature is measured when a measuring instrument is brought into contact with the medium being measured (e.g., a thermometer). All temperature-measuring instruments use some change in a material to indicate temperature. Some of the effects that are used to indicate temperature are changes in physical properties and altered physical dimensions (e.g., the change in the length of a material in the form of expansion and contraction).

Several temperature scales have been developed to provide a standard for indicating the temperatures of substances. The most commonly used scales include the Fahrenheit, Celsius, Kelvin, and Rankine temperature scales. The Celsius scale is also called the centigrade scale.

The Fahrenheit (ÂşF) and Celsius (ÂşC) scales are based on the freezing point and boiling point of water. The freezing point of a substance is the temperature that changes its physical state from a liquid to a solid. The boiling point is the temperate that a substance changes from a liquid state to a gaseous state.

Note: Thermometers are classified as mechanical temperature sensing devices because they produce some type of mechanical action or movement in response to temperature changes. There are many types of thermometers: liquid, gas, and vapor filled systems and bimetallic thermometers.

8.10.1.1.5.1

Industrial Thermometers

Figure 8.44 shows an industrial-type thermometer that is commonly used for measuring the temperature of fluids

Thermometer

Capillary tube

Scale Union fitting

Bulb

FIGURE 8.44 Industrial thermometer. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Š 2003 by CRC Press LLC

Pointer Scale

Bimetallic element

FIGURE 8.45 Bimetallic gauge. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

in industrial piping systems. This type of measuring instrument is nothing more than a rugged version of the familiar mercury thermometer. The bulb and capillary tube are contained inside a protective metal tube called a well.

The thermometer is attached to the piping system (vat, tank, or other component) by a union fitting.

8.10.1.1.5.2

Bimetallic Gauge Thermometer

Another common type of temperature gauge is the bimetallic gauge shown in Figure 8.45. Bimetallic means that if two materials with different linear coefficients of expansion (i.e., how much a material expands with heat) are bonded together, as the temperature changes their rate of expansion will be different. This will cause the entire assembly to bend in an arc. When the temperature is raised, an arc is formed around the material with the smaller expansion coefficient. The amount of arc is reflected in the movement of the pointer on the gauge.

Because two dissimilar materials form the assembly, it is known as a bimetallic element, which is also commonly used in thermostats.

8.10.2 VACUUM BREAKERS Another common ancillary device found in pipelines is a vacuum breaker (components shown in Figure 8.46). Simply, a vacuum breaker is a mechanical device that allows air into the piping system, thereby preventing backflow that could otherwise be caused by the siphoning action created by a partial vacuum. In other words, a vacuum breaker is designed to admit air into the line whenever a vacuum develops. A vacuum, obviously, is the absence of air. Vacuum in a pipeline can be a serious problem. For example, it can cause fluids to run in the wrong direction, possibly mixing contaminants with purer solutions. (Note: In water systems, backsiphonage can occur when a partial vacuum pulls nonpotable liquids back into the supply lines.44) In addition, it can cause the collapse of tubing or equipment.

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Body Retainer tube Spring

Ball

Seat

FIGURE 8.46 Vacuum breaker components. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

As illustrated in Figure 8.46, this particular type of vacuum breaker uses a ball that usually is held against a seat by a spring. The ball is contained in a retainer tube mounted inside the piping system or inside the component being protected. If a vacuum develops, the ball is forced (sucked) down into the retainer tube, where it works against the spring. Air flows into the system to fill the vacuum. (Note: In water systems, when air enters the line between a cross-connection and the source of the vacuum, then the vacuum will be broken and backsiphonage is prevented.45) The spring then returns the ball to its usual position, which acts to seal the system again.

8.10.3 ACCUMULATORS As mentioned, in a plant compressed air system, a means of storing and delivering air as needed is usually provided.

An air receiver normally accomplishes this. In a hydraulic system, an accumulator provides the functions provided by an air receiver for an air system. The accumulator (usually a dome-shaped or cylindrical chamber or tank attached to a hydraulic line) in a hydraulic system works to help store and deliver energy as required. Moreover, accumulators work to help keep pressure in the line smoothed out. For example, if pressure in the line rises suddenly, the accumulator absorbs the rise, preventing shock to the piping. If pressure in the line drops, the accumulator acts to bring it up to normal.

Important Point: The primary function of an accumulator in a hydraulic system is to supplement pump flow.

8.10.4 AIR RECEIVERS As shown in Figure 8.47, an air receiver is a tank or cylindrical-type vessel used for a number of purposes.

Most important is their ability to store compressed air.

Much like accumulators, they cushion shock from sudden pressure rises in an airline. The air receiver serves to absorb the shock of valve closure and load starts, stops, and reversals. There is no liquid in an air receiver. The air compresses as pressure rises. As pressure drops, the air expands to maintain pressure in the line. © 2003 by CRC Press LLC

FIGURE 8.47 Air receiver. (From Spellman, F.R. and Drinan, J., Piping and Valves, Technomic Publ., Lancaster, PA, 2001.)

Important Note: OSHA has a standard, 29 CFR 1910.169(a), requiring air receivers be drained.

Specifically, the standard states, “a drain pipe and valve shall be installed at the lowest point of every air receiver to provide for the removal of accumulated oil and water.”46 This is an item that should be taken seriously, not only for safety reasons, but also because it is a compliance item that OSHA inspectors often check.

8.10.5 HEAT EXCHANGERS Operating on the principle that heat flows from a warmer body to a cooler one, heat exchangers are devices used for adding or removing heat and cold from a liquid or gas.

The purpose may be to cool one body or warm the other; nonetheless, whether used to warm or to cool, the principle remains the same. Various designs are used in heat exchangers. The simplest form consists of a tube, or possibly a large coil of tubing, placed inside a larger cylinder.

In an oil lubrication system, the purpose of a heat exchanger is to cool the hot oil. A heat exchanger system can also be used to heat up a process fluid circulating through part of the heat exchanger while steam circulates through its other section.

Final Note: In this section, we have discussed the major ancillary or accessory equipment used in many piping systems. It is important to point out that there are other accessories commonly used in piping systems (e.g., rotary pressure joints, actuators, intensifiers, pneumatic pressure

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line accessories, and so forth); however, discussion of these accessories is beyond the scope of this text.

8.11 CHAPTER REVIEW QUESTIONS AND PROBLEMS 8.1. What is an expansion joint?

8.2. A _______ is defined as any substance or material that flows.

8.3. Compressed air is considered to be a _________.

8.4. Sections or lengths of pipe are ___________ with fittings.

8.5. The _______ of fluids through a pipe is controlled by valves.

8.6. Friction causes __________________ in a piping system.

8.7. As friction __________ in a piping system, the output pressure decreases.

8.8. Relief valves are designed to open ______________.

8.9. ____________ is used to help keep the fluids carried in piping systems hot or cold.

8.10. The major problems in piping systems are caused by _________ and corrosion.

8.11. If the speed of fluid in a pipe doubled, the friction is _____________.

8.12. The most important factor in keeping a piping system operating efficiently is _________.

8.13. Pipe sizes above __________ in. are usually designated by outside diameter.

8.14. The difference in __________ numbers represents the difference in the wall _________ of pipes.

8.15. When pipe wall thickness ___________, the I.D. decreases.

8.16. A _________ metal contains iron.

8.17. As temperature ____________, the viscosity of a liquid decreases.

8.18. What is another name for rust?

8.19. Sections of __________ water pipe are usually connected with a bell-and-spigot joint.

8.20. A ferrous metal always contains _________.

8.21. Asbestos-cement pipe has the advantage of being highly resistant to ______________.

8.22. As temperature increases, the strength of plastic pipe ___________.

8.23. Name four basic nonmetallic piping materials.

8.24. Vitrified clay pipe is the most ____________ pipe available for carrying industrial wastes.

8.25. Cast iron pipe can be lined with __________ to increase its resistance to corrosion.

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8.26. A joint made so that the sections of tubing are __________ together is called a compression joint.

8.27. Incorrect tube bends can cause ___________ flow and _________ pressure.

8.28. High-pressure hydraulic systems use ______ tubing.

8.29. One process used to join plastic tubing is called ________ welding.

8.30. Compared to pipe, tubing is more ________.

8.31. ___________ tubing is most likely used in food-processing applications.

8.32. Before tubing can be bent or flared, it should be __________.

8.33. Plastic tubing is usually joined by ________.

8.34. The materials used most commonly for tubing are __________ and _________.

8.35. Smooth fluid flow is called _________ flow.

8.36. The ___________ hose is the most common type of hose in general use.

8.37. The type of hose construction most suitable for maximum suction conditions is _______.

8.38. __________ is the nonmetallic hose best suited for use at extremely low temperatures.

8.39. Each size of hose clamp is designed for a hose of a specific ____________.

8.40. ___________ is the outstanding advantage of hose.

8.41. Applied to a hose, the letters ____________ stand for enlarged end.

8.42. A hose is __________ in order to provide strength and greater resistance to ________.

8.43. The Dacron hose remains _________ at extremely low temperatures.

8.44. The ______________ fitting allows for a certain amount of pipe movement.

8.45. The ______________ fitting helps reduce the effects of water hammer.

8.46. A flange that has a plain face should be joined to a flange that has a ____________ face.

8.47. Improperly made ___________ restrict fluid flow in a pipeline.

8.48. The designation 200 lb refers to the _______ at which a fitting can safely be used.

8.49. Used to close off an unused outlet in a fitting with a _____________.

8.50. A ______ connects two or more pipes of a different diameter.

8.51. A ____________ is used to make a pressuretight joint between ______________ has a more gradual curve than does the shortradius elbow.

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8.52. _________ control fluid flow through piping systems.

8.53. Valves can be used to _________, ________, and _______ flow.

8.54. A ________ valve is better suited for throttling service than is a gate valve.

8.55. A _______ valve is a fast-operating shut-off valve commonly used in large water-circulating systems.

8.56. A pressure regulating valve keeps the _________ at a _______ level.

8.57. ____________ in a fluid line can clog the closing element of a valve.

8.58. Before removing a strainer for cleaning, the line should be ___________.

8.59. Because steam traps operate in a mixture of steam and water it is often difficult to ____________ steam traps.

8.60. Steam traps are used to remove __________ or ___________ from steam lines.

8.61. ____________ is steam that condenses into water in a piping system.

8.62. __________ pressure is equal to gauge pressure plus atmospheric pressure.

8.63. _____________ pressure gauges do not provide extremely accurate readings.

8.64. The value that represents how much a material __________ is called the coefficient of expansion.

8.65. The purpose of a ____________ is to admit air into the system.

REFERENCES 1. Kawamura, S., Integrated Design and Operation of Water Treatment Facilities, 2nd ed., John Wiley & Sons, Inc., New York, 1999, pp. 241–242.

2. Nayyar, M.L., Introduction to piping, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. A-3.

3. Magnusson, R.J., Technology in the Middle Ages, The John Hopkins University, Baltimore, 2001, p. 63.

4. Kawamura, S., Integrated Design and Operation of Water Treatment Facilities, 2nd ed., John Wiley & Sons, Inc., New York, 1999, p. 481.

5. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 211.

6. Adapted from McGhee, T.J., Water Supply and Sewage, 6th ed., McGraw-Hill, New York, 1991, p. 297.

7. Nayyar, M.L., Introduction to piping, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. A-4.

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8. American Society of Mechanical Engineers, ASME b36.10M, Welded and Seamless Wrought Steel Pipe, New York, 1996, B 111; ASME B36.19M, Stainless Steel Pipe, New York, 1985 B 113.

9. Nayyar, M.L., Piping fundamentals, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. A-7.

10. Steam: Its Generation and Use, The Babcock & Wilcox Company, Cambridge, Ontario, 1972, p. 23.

11. Snoek, P.E. and Carney, J.C., Pipeline Material Selection for Transport of Abrasive Tailings, Proc. 6th International Tech. Conf. on Slurry Transp., Las Vegas, NV, March 24–27, 1981.

12. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 27.

13. Gagliardi, M.G. and Liberatore, L.J., Water piping systems, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. C-26.

14. Gagliardi, M.G. and Liberatore, L.J., Water piping systems, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. C-28.

15. Gagliardi, M.G. and Liberatore, L.J., Water piping systems, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. C-32.

16. Marine, C.S., Hydraulic transient design for pipeline systems, in Water Distribution Systems Handbook, Mays, L.W., Ed., McGraw-Hill, New York, 1999, p. 6.1.

17. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, pp. 239–241.

18. Crocker, S., Jr., Hierarchy of design documents, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGrawHill, New York, 2000, p. B-28.

19. Crocker, S., Jr., Hierarchy of design documents, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGrawHill, New York, 2000, p. B-30.

20. McGhee, T.J., Water Supply and Sewerage, 6th ed., McGraw-Hill, New York, 1991, pp. 297–298.

21. American Concrete Pipe Association, Concrete Pipe Design Manual, Vienna, VA, 1987, p. 44.

22. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, pp. 51–52.

23. Asbestos Awareness, Coastal Video Communications Corp., Virginia Beach, VA, 1994, p. 2.

24. Bales, R.C., NewKirk, D.D., and Hayward, S.B., Chrysoltile asbestos in California surface waters: from upstream rivers through water treatment, J. Am. Water Works Assoc., 76, 66, 1984.

25. Webber, J.S., Covey, J.R., and King, M.V., Asbestos in drinking water supplied through grossly deteriorated pipe, J. Am. Water Works Assoc., 81, 80, 1989.

26. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 44.

27. McGhee, T.J., Water Supply and Sewerage, 6th ed., McGraw-Hill, New York, 1991, p. 121.

28. Asbestos Awareness, Coastal Video Communications Corp., Virginia Beach, VA, 1994, p. 9.

29. Spellman, F.R., Safe Work Practices for Wastewater Treatment Plants, Technomic Publ., Lancaster, PA, 1996, pp. 201–202.

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30. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 45.

31. Lohmeir, A. and Avery, D.R., Manufacture of metallic pipe, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. A-357.

32. Basavaraju, C., Pipe properties; Geiger, E.L., Tube properties, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, pp. E-13–E-36.

33. McGhee, T.J., Water Supply and Sewerage, 6th ed., McGraw-Hill, New York, 1991, p. 25.

34. Adapted from Giachino, J.W. and Weeks, W., Welding Skills, American Technical Publishers, Homewood, IL, 1985, pp. 284–289.

35. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 258.

36. Geiger, E.L., Piping components, in Piping Handbook, 7th ed., Nayyar, M.L., Ed., McGraw-Hill, New York, 2000, p. A-53.

37. Valves, Integrated Publishing’s official web page, http://tpub.com/fluid/ch2c.htm, 1998, chap. 6, pp. 1–4.

38. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 61.

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39. Globe Valves, Integrated Publishing’s official web page, http://tpub.com/fluid/ch2c.htm, 1998, chap. 6, p. 2.

40. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 77.

41. Casada, D., Control Valve Replacement Savings, Oak Ridge National Laboratory, Oak Ridge, TN, pp. 1-3, 2000.

42. Sections 8.2 & 8.3 adapted from Geiger, E.L., Piping Components and Frankel, M., Compressed Air Piping Systems. In Piping Handbook, 7th ed., Nayyar, M.L., (ed.). New York: McGraw-Hill, pp. A.53–A.83, C.755–C.777, 2000.

43. Adapted from Bandes, A. and Gorelick, B., Inspect Steam Traps for Efficient System, TWI Press, Terre Haute, Indiana: 2000, pp. 1–4.

44. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, pp. 336–337.

45. American Water Works Association, Water Transmission and Distribution, 2nd ed., Denver, CO, 1996, p. 336.

46. Occupational Safety and Health Administration, OSHA Directive STD 1.10.2: Drain on Air Receivers; 29 CFR 1910.169(a)(2)(I) and (6)(2), U.S. Department of Labor, Washington, D.C., October 30, 1978, pp. 1–3.